• Breaking Change Null Safety is now enabled by default in all packages with a lower sdk constraint of 2.12.0 or greater. Files that are not subject to language versioning (whether because they are not contained in a pub package, or because the package that they are contained in has no lower sdk constraint) are treated as opted into to null safety by default and may report new errors. Pub packages may be opted out of null safety by setting a min sdk constraint in pubspec.yaml of 2.9.0 or less. Files may be opted out of null safety by adding // @dart=2.9 to the beginning of the file.

  • Breaking Change #44660: Fixed an implementation bug where this would sometimes undergo type promotion in extensions.

Core libraries


  • Adds extension method onError on Future to allow better typing of error handling.


  • Added UnmodifiableSetView class, which allows users to guarantee that methods that could change underlying Set instance can not be invoked.

  • LinkedList made it explicit that elements are compared by identity, and updated contains to take advantage of this.


  • Added unmodifiable constructor to class Set, which allows users to create unmodifiable Set instances.


  • HttpRequest will now correctly follow HTTP 308 redirects (HttpStatus.permanentRedirect).


  • Added debugName positional parameter to ReceivePort and RawReceivePort constructors, a name which can be associated with the port and displayed in tooling.


  • EventStreamSubscription.cancel has been updated to retain its synchronous timing when running in both sound and unsound null safety modes. See issue #44157 for more details.

Dart VM

  • Breaking Change #42312: Dart_WeakPersistentHandles will no longer auto-delete themselves when the referenced object is garbage collected to avoid race conditions, but they are still automatically deleted when the isolate group shuts down.
  • Breaking Change #42312: Dart_WeakPersistentHandleFinalizer is renamed to Dart_HandleFinalizer and had its handle argument removed. All api functions using that type have been updated.

Foreign Function Interface (dart:ffi)

  • Breaking Change #44621: Invocations with a generic T of sizeOf<T>, Pointer<T>.elementAt(), Pointer<T extends Struct>.ref, and Pointer<T extends Struct>[] are being deprecated in the current stable release (2.12), and are planned to be fully removed in the following stable release (2.13). Consequently, allocate in package:ffi will no longer be able to invoke sizeOf<T> generically, and will be deprecated as well. Instead, the Allocator it is introduced to dart:ffi, and also requires a constant T on invocations. For migration notes see the breaking change request.
  • Breaking Change #44622: Subtypes of Struct without any native member are being deprecated in the current stable release (2.12), and are planned to be fully removed in the following stable release (2.13). Migrate opaque types to extend Opaque rather than Struct.


  • Removed --no-defer-class-types and --no-new-deferred-split.



  • Removed the --use-fasta-parser, --preview-dart-2, and --enable-assert-initializers command line options. These options haven't been supported in a while and were no-ops.
  • Report diagnostics regarding the @internal annotation.
  • Improve diagnostic-reporting regarding the @doNotStore annotation.
  • Introduce a diagnostic which is reported when a library member named main is not a function.
  • Introduce a diagnostic which is reported when a main function's first parameter is not a supertype of List<String>.
  • Introduce a diagnostic which is reported when an // ignore comment contains an error code which is not being reported.
  • Introduce a diagnostic which is reported when an // ignore comment contains an error code which cannot be ignored.
  • Introduce a diagnostic which is reported when an // ignore comment contains an error code which is already being ignored.
  • Report diagnostics when using @visibleForTesting on top-level variables.
  • Fix false positive reports of “unused element” for top-level setters and getters.
  • Fix false positive reports regarding @deprecated field formal parameters at their declaration.
  • For null safety, introduce a diagnostic which reports when a null-check will always fail.
  • Fix false positive reports regarding optional parameters on privat constructors being unused.
  • Introduce a diagnostic which is reported when a constructor includes duplicate field formal parameters.
  • Improve the “unused import” diagnostic when multiple import directives share a common prefix.
  • Fix false positive “unused import” diagnostic regarding an import which provides an extension method which is used.
  • For null safety, improve the messaging of “use of nullable value” diagnostics for eight different contexts.
  • Fix false positive reports regarding @visibleForTesting members in a “hide” combinator of an import or export directive.
  • Improve the messaging of “invalid override” diagnostics.
  • Introduce a diagnostic which is reported when Future<T>.catchError is called with an onError callback which does not return FutureOr<T>.


  • Don't duplicate comments on chained if elements.
  • Preserve ? in initializing formal function-typed parameters.


Updated the Linter to 0.1.129, which includes:

  • New lint: avoid_dynamic_calls.
  • (Internal): avoid_type_to_string updated to use addArgumentList registry API.
  • Miscellaneous documentation improvements.
  • Fixed crash in prefer_collection_literals when there is no static parameter element.
  • Fixed false negatives for prefer_collection_literals when a LinkedHashSet or LinkedHashMap instantiation is passed as the argument to a function in any position other than the first.
  • Fixed false negatives for prefer_collection_literals when a LinkedHashSet or LinkedHashMap instantiation is used in a place with a static type other than Set or Map.
  • (Internal): test updates to the new PhysicalResourceProvider API.
  • Fixed false positives in prefer_constructors_over_static_methods.
  • Updates to package_names to allow leading underscores.
  • Fixed NPEs in unnecessary_null_checks.
  • A fixed NPE in missing_whitespace_between_adjacent_strings.
  • Updates to void_checks for NNBD.
  • A fixed range error in unnecessary_string_escapes.
  • A fixed false positives in unnecessary_null_types.
  • Fixes to prefer_constructors_over_static_methods to respect type parameters.
  • Updates to always_require_non_null_named_parameters to be NNBD-aware.
  • Updates tp unnecessary_nullable_for_final_variable_declarations to allow dynamic.
  • Updates overridden_fields to not report on abstract parent fields.
  • Fixes to unrelated_type_equality_checks for NNBD.
  • Improvements to type_init_formalsto allow types not equal to the field type.
  • Performance improvements to always_use_package_imports, avoid_renaming_method_parameters, prefer_relative_imports and public_member_api_docs.
  • (internal): updates to analyzer 0.40.4 APIs
  • New lint: cast_nullable_to_non_nullable.
  • New lint: null_check_on_nullable_type_parameter.
  • New lint: tighten_type_of_initializing_formals.
  • Updates to public_member_apis to check generic type aliases.
  • (Internal): updates to adopt new analyzer APIs.
  • Fixed close_sinks to handle this-prefixed property accesses.
  • New lint: unnecessary_null_checks.
  • Fixed unawaited_futures to handle Future subtypes.
  • New lint: avoid_type_to_string.


  • Breaking: The Dart SDK constraint is now required in pubspec.yaml.

    You now have to include a section like:

      sdk: '>=2.10.0 <3.0.0'

    See #44072.

    For legacy dependencies without an sdk constraint pub will now assume a default language version of 2.7.

  • The top level pub executable has been deprecated. Use dart pub instead. See dart tool.

  • New command dart pub add that adds new dependencies to your pubspec.yaml.

    And a corresponding dart pub remove that removes dependencies.

  • New option dart pub upgrade --major-versions will update constraints in your pubspec.yaml to match the the resolvable column reported in dart pub outdated. This allows users to easily upgrade to latest version for all dependencies where this is possible, even if such upgrade requires an update to the version constraint in pubspec.yaml.

    It is also possible to only upgrade the major version for a subset of your dependencies using dart pub upgrade --major-versions <dependencies...>.

  • New option dart pub upgrade --null-safety will attempt to update constraints in your pubspec.yaml, such that only null-safety migrated versions of dependencies are allowed.

  • New option dart pub outdated --mode=null-safety that will analyze your dependencies for null-safety.

  • dart pub get and dart pub upgrade will highlight dependencies that have been discontinued on pub.dev.

  • dart pub publish will now check your pubspec keys for likely typos.

  • dart pub upgrade package_foo will fetch dependencies, but ignore the pubspec.lock for package_foo, allowing users to only upgrade a subset of dependencies.

  • New command dart pub login that logs in to pub.dev.

  • The --server option to dart pub publish and dart pub uploader have been deprecated. Use publish_to in your pubspec.yaml or set the $PUB_HOSTED_URL environment variable.

  • `pub global activate no longer re-precompiles if current global installed was same version.

  • The Flutter SDK constraint upper bound is now ignored in pubspecs and deprecated when publishing.

    See: flutter-upper-bound-deprecation.

2.10.5 - 2020-01-21

This is a patch release that fixes a crash in the Dart VM. (issue #44563).

2.10.4 - 2020-11-12

This is a patch release that fixes a crash in the Dart VM (issues #43941, flutter/flutter#43620, and Dart-Code/Dart-Code#2814).

2.10.3 - 2020-10-29

This is a patch release that fixes the following issues:

2.10.2 - 2020-10-15

This is a patch release that fixes a DDC compiler crash (issue #43589).

2.10.1 - 2020-10-06

This is a patch release that fixes the following issues:

  • crashes when developing Flutter applications (issue #43464).
  • non-deterministic incorrect program behaviour and/or crashes (issue flutter/flutter#66672).
  • uncaught TypeErrors in DDC (issue #43661).

2.10.0 - 2020-09-28

Core libraries


  • Adds Abort method to class HttpClientRequest, which allows users to cancel outgoing HTTP requests and stop following IO operations.
  • A validation check is added to path of class Cookie. Having characters ranging from 0x00 to 0x1f and 0x3b (“;”) will lead to a FormatException.
  • The HttpClient and HttpServer classes now have a 1 MiB limit for the total size of the HTTP headers when parsing a request or response, instead of the former 8 KiB limit for each header name and value. This limit cannot be configured at this time.


  • Class BytesBuilder is moved from dart:io to dart:typed_data. It's temporarily being exported from dart:io as well.


  • [#42564]: Solved inconsistency in Uri.https and Uri.http constructors' queryParams type.

Dart VM

  • Breaking Change #42982: dart_api_dl.cc is renamed to dart_api_dl.c and changed to a pure C file.
  • Introduces Dart_FinalizableHandles. They do auto-delete, and the weakly referred object cannot be accessed through them.


  • Adds support for deferred loading of types seperately from classes. This enables dart2js to make better optimization choices when deferred loading. This work is necessary to address unsoundness in the deferred loading algorithm. Currently, fixing this unsoundness would result in code bloat, but loading types seperately from classes will allow us to fix the unsoundness with only a minimal regression. To explicitly disable deferred loading of types, pass --no-defer-class-types. See the original post on the unsoundness in the deferred loading algorithm.
  • Enables a new sound deferred splitting algorithm. To explicitly disable the new deferred splitting algorithm, pass --no-new-deferred-split. See the original post on the unsoundness in the deferred loading algorithm.



  • Don't crash when non-ASCII whitespace is trimmed.
  • Split all conditional expressions (?:) when they are nested.
  • Handle external and abstract fields and variables.


Updated the Linter to 0.1.118, which includes:

  • New lint: unnecessary_nullable_for_final_variable_declarations.
  • Fixed NPE in prefer_asserts_in_initializer_lists.
  • Fixed range error in unnecessary_string_escapes.
  • unsafe_html updated to support unique error codes.
  • Updates to diagnostic_describe_all_properties to check for Diagnosticables (not DiagnosticableMixins).
  • New lint: use_late.
  • Fixed unnecessary_lambdas to respect deferred imports.
  • Updated public_member_api_docs to check mixins.
  • Updated unnecessary_statements to skip as expressions.
  • Fixed prefer_relative_imports to work with path dependencies.


  • pub run and pub global run accepts a --(no-)-sound-null-safety flag, that is passed to the VM.
  • Fix: Avoid multiple recompilation of binaries in global packages.
  • Fix: Avoid exponential behaviour of error reporting from the solver.
  • Fix: Refresh binstubs after recompile in global run.

2.9.3 - 2020-09-08

This is a patch release that fixes DDC to handle a breaking change in Chrome (issue #43193).

2.9.2 - 2020-08-26

This is a patch release that fixes transient StackOverflow exceptions when building Flutter applications (issue flutter/flutter#63560).

2.9.1 - 2020-08-12

This is a patch release that fixes unhandled exceptions in some Flutter applications (issue flutter/flutter#63038).

2.9.0 - 2020-08-05


Core libraries


  • Adds Stream.multi constructor creating streams which can be listened to more than once, and where each individual listener can be controlled independently.


  • Breaking Change #41100: When encoding a string containing unpaired surrogates as UTF-8, the unpaired surrogates will be encoded as replacement characters (U+FFFD). When decoding UTF-8, encoded surrogates will be treated as malformed input. When decoding UTF-8 with allowMalformed: true, the number of replacement characters emitted for malformed input sequences has been changed to match the WHATWG encoding standard.


  • #42006: The signature of exit has been changed to return the Nevertype instead of void. since no code will run after it,
  • Class OSError now implements Exception. This change means OSError will now be caught in catch clauses catching Exceptions.
  • Added InternetAddress.tryParse.
  • Abstract Unix Domain Socket is supported on Linux/Android now. Using an InternetAddress with address starting with ‘@’ and type being InternetAddressType.Unix will create an abstract Unix Domain Socket.
  • On Windows, file APIs can now handle files and directories identified by long paths (greater than 260 characters). It complies with all restrictions from Long Path on Windows. Note that Directory.current does not work with long path.


  • Breaking Change: CssClassSet.add() previously returned null if the CssClassSet corresponded to multiple elements. In order to align with the null-safe changes in the Set interface, it will now return false instead. The same applies for CssClassSet.toggle.

  • EventStreamSubscription.cancel method used to return null, but since StreamSubscription.cancel has changed to be non-nullable, this method returns an empty Future instead. Due to an optimization on null Futures, this method used to complete synchronously, but now that the Future is empty instead, it completes asynchronously, therefore potentially invalidating code that relied on the synchronous side-effect. This change will only affect code using sound null-safety. See issue #41653 for more details.

  • Methods in Console have been updated to better reflect the modern Console specification. Particularly of interest are dir and table which take in extra optional arguments.


  • Breaking Change #42714: web compilers (dart2js and DDC) now produce a compile-time error if dart:mirrors is imported.

    Most projects should not be affected. Since 2.0.0 this library was unsupported and produced runtime errors on all its APIs. Since then several tools already reject code that use dart:mirrors including webdev and flutter tools, we expect few projects to run into this problem.



  • Add --fix-single-cascade-statements.
  • Correctly handle var in --fix-function-typedefs.
  • Preserve leading indentation in fixed doc comments.
  • Split outer nested control flow elements.
  • Always place a blank line after script tags.
  • Don't add unneeded splits on if elements near comments.
  • Indent blocks in initializers of multiple-variable declarations.
  • Update the null-aware subscript syntax from ?.[] to ?[].


Updated the Linter to 0.1.117, which includes:

  • New lint: do_not_use_environment.
  • New lint: exhaustive_cases.
  • New lint: no_default_cases (experimental).
  • New lint: sized_box_for_whitespace.
  • New lint: use_is_even_rather_than_modulo.
  • Updated directives_ordering to remove third party package special-casing.
  • Updated prefer_is_empty to special-case assert initializers and const contexts.
  • Updated prefer_mixin to allow “legacy” SDK abstract class mixins.
  • Updated sized_box_for_whitespace to address false-positives.
  • Updated type_annotate_public_apis to allow inferred types in final field assignments.
  • Updated unnecessary_lambdas to check for tear-off assignability.
  • Updated unsafe_html to use a SecurityLintCode (making it un-ignorable) and to include Window.open, Element.html and DocumentFragment.html in unsafe API checks. Also added checks for attributes and methods on extensions.

Dart VM

  • Breaking Change #41100: When printing a string using the print function, the default implementation (used when not overridden by the embedder or the current zone) will print any unpaired surrogates in the string as replacement characters (U+FFFD). Similarly, the Dart_StringToUTF8 function in the Dart API will convert unpaired surrogates into replacement characters.


  • pub run and pub global run accepts a --enable-experiment flag enabling experiments in the Dart VM (and language).
  • Warn when publishing the first null-safe version of a package.
  • pub outdated:
    • If the current version of a dependency is a prerelease version, use prereleases for latest if there is no newer stable.
    • Don't require a pubspec.lock file. When the lockfile is missing, the Current column is empty.
  • pub upgrade: Show summary count of outdated packages after running. It will also only show newer packages if they are not prereleases or the package is already a prerelease.
  • Publishing Flutter plugins using the old plugin format is no longer allowed. Plugins using the old plugin format can still be consumed.
  • pub run: Fix precompilation with relative PUB_CACHE paths (#2486).
  • Preserve Windows line endings in pubspec.lock if they are already there (#2489).
  • Better terminal color-detection. Use colors in terminals on Windows.
  • Fix git folder names in cache, allowing for ssh-style git dependencies.
  • Fix: Avoid precompilation of dependencies of global packages.

2.8.4 - 2020-06-04

This is a patch release that fixes potential memory leaks in the Dart front-end (issues #42111 and #42112).

2.8.3 - 2020-05-28

This is a patch release that fixes the following issues:

2.8.2 - 2020-05-13

This is a patch release that fixes an AOT compilation bug in global transformations which manifests as a NoSuchMethod exception (issue flutter/flutter#56479).

2.8.1 - 2020-05-06

Much of the changes in this release are in preparation for non-nullable types, which will arrive in a future version. In anticipation of that, we have made a number of small but technically breaking changes to several core library APIs in order to make them easier to use in a world with non-nullable types. Almost all existing Dart code will be unaffected by these changes, but if you see unexpected failures, note the breaking changes listed below.


There are no new language features in this release. There are only two minor breaking changes:

  • Breaking change #40675: Fixed an implementation bug where local variable inference would incorrectly use the promoted type of a type variable.

  • Breaking change #41362: Dart 2.0.0 made the clauses implements Function, extends Function, or with Function have no effect (spec section 19.6). We fixed an implementation bug that may be visible on some rare scenarios.

Core libraries


  • Breaking change #40676: Changed the return type of StreamSubscription.cancel() to Future<void>. Previously, it was declared to return Future and was allowed to return null at runtime.

  • Breaking change #40681: The runZoned() function is split into two functions: runZoned() and runZonedGuarded(), where the latter has a required onError parameter, and the former has none. This prepares the functions for Null Safety where the two functions will differ in the nullability of their return types.

  • Breaking change #40683: Errors passed to Completer.completeError(), Stream.addError(), Future.error(), etc. can no longer be null. These operations now synchronously throw an exception if passed a null error.

  • Make stack traces non-null #40130. Where methods like completer.completeError() allow omitting a stack trace, the platform will now insert a default stack trace rather than propagate a null value.

    Error handling functions need no longer be prepared for null stack traces.


  • Breaking change #40674: Three members on RuneIterator no longer return null when accessed before the first call to moveNext(). Instead, current and rawIndex return -1 and currentAsString returns an empty string.

  • Breaking change #40678: The String.fromEnvironment() default value for defaultValue is now an empty string instead of null. Likewise, the default value for int.fromEnvironment()'s defaultValue parameter is zero. Under null safety, a constructor cannot return null, so this prepares these APIs for that.

  • The class CastError is deprecated, and all implementation specific classes implementing TypeError or CastError now implement both. In a future release, CastError will be removed. See issue 40763 for details.

  • Adds StackTrace.empty constant which is the stack trace used as default stack trace when no better alternative is available.

  • The class TypeError no longer extends AssertionError. This also means that it no longer inherits the spurious message getter which was added to AssertionError when the second operand to assert was allowed. The value of that getter on a TypeError was the same string as returned by toString(), so it is still available.

  • ArgumentError.checkNotNull() and the RangeError static methods checkValueInInterval(), checkValidIndex() and checkNotNegative() all return their first argument on success. This makes these functions more convenient to use in-line in, for example, => function bodies or constructor initialization lists.


  • The constructors for TimelineTask now accept an optional filterKey parameter. If provided, the arguments for all events associated with the task will contain an entry named filterKey, set to the value of the filterKey parameter provided in the constructor. This will be used by tooling to allow for better filtering of timeline events.


  • Breaking Change #39627: Changed the return type of several HTML native methods involving futures. In return types that matched Future<List<T>>, T was changed to dynamic. These methods would have resulted in a runtime error if they were used.

  • Breaking Change: Node.insertAllBefore() erroneously had a return type of Node, even though it was not returning anything. This has been corrected to void.


  • Class HttpParser will no longer throw an exception when a HTTP response status code is within [0, 999]. Customized status codes in this range are now valid.

  • Breaking change #33501: The signature of HttpHeaders methods add() and set have been changed to:

    void add(String name, Object value, {bool preserveHeaderCase: false})
    void set(String name, Object value, {bool preserveHeaderCase: false})

    Setting preserveHeaderCase to true preserves the case of the name parameter instead of converting it to lowercase. The HttpHeader.forEach() method provides the current case of each header.

    This is breaking only for classes extending or implementing HttpHeaders and having their own add or set methods without the bool preserveHeaderCase named parameter.

  • Breaking change #40702: The Socket class now throws a SocketException if the socket has been explicitly destroyed or upgraded to a secure socket upon setting or getting socket options. Previously, setting a socket option would be ignored and getting a socket option would return null.

  • Breaking change #40483: The Process class now throws a StateError if the process is detached (ProcessStartMode.detached and ProcessStartMode.detachedWithStdio) upon accessing the exitCode getter. It now also throws when not connected to the child process's stdio (ProcessStartMode.detached and ProcessStartMode.inheritStdio) upon accessing the stdin, stdout, and stderr getters. Previously, these getters would all return null.

  • Breaking change #40706: The dummy object returned if FileStat.stat() or FileStat.statSync() fail now contains Unix epoch timestamps instead of null for the accessed, changed, and modified getters.

  • Breaking change #40709: The HeaderValue class now parses more strictly in two invalid edge cases. This is the class used to parse the semicolon delimited parameters used in the Accept, Authorization, Content-Type, and other such HTTP headers.

    The empty parameter value without double quotes (which is not allowed by the standards) is now parsed as the empty string rather than null. E.g. HeaderValue.parse("v;a=").parameters now gives {"a": ""} rather than {"a": null}.

    Invalid inputs with unbalanced double quotes are now rejected. E.g. HeaderValue.parse('v;a="b').parameters will now throw a HttpException instead of giving {"a": "b"}.

  • The HeaderValue.toString() method now supports parameters with null values by omitting the value. HeaderValue("v", {"a": null, "b": "c"}).toString() now gives v; a; b=c. This behavior can be used to implement some features in the Accept and Sec-WebSocket-Extensions headers.

    Likewise the empty value and values using characters outside of RFC 7230 tokens are now correctly implemented by double quoting such values with escape sequences. For example:

        {"a": "A", "b": "(B)", "c": "", "d": "ø", "e": "\\\""}).toString()

    Gives: v;a=A;b="(B)";c="";d="ø";e="\\\"".

  • Unix domain sockets are now supported on Linux, Android and MacOS, which can be used by passing a InternetAddress of InternetAddressType.Unix into the connect(), startConnect() and bind() methods. The port argument in those methods will be ignored. The port getter always returns 0 for Unix domain sockets.

  • Class InternetAddressType gains one more option Unix, which represents a Unix domain address.

  • Class InternetAddress:

    • InternetAddress constructor gains an optional type parameter. To create a Unix domain address, type is set to InternetAddressType.Unix and address is a file path.

    • InternetAddress gains a new constructor fromRawAddress() that takes an address in byte format for Internet addresses or raw file path for Unix domain addresses.

  • Breaking change #40681: The static methods runZoned() and runWithHttpOverrides() on HttpOverrides no longer accept zoneSpecification and onError parameters. Use the runZoned() or runZonedGuarded() functions from dart:async directly if needing to specify those.

  • Class HttpClient and HttpServer, when receiving HttpRequest or HttpClientResponse, will now put a 8K size limit on its header fields and values.


  • Added MirrorSystem.neverType.

Dart VM

  • Added Dart_TypeDynamic, Dart_TypeVoid and Dart_TypeNever. Type dynamic can no longer by reached using Dart_GetType(dart:core, dynamic).

  • Added the following methods to the VM embedding API:

    • Dart_GetNonNullableType()
    • Dart_GetNullableType()
    • Dart_TypeToNonNullable()
    • Dart_TypeToNullable()
    • Dart_IsLegacyType()
    • Dart_IsNonNullableType()
    • Dart_IsNullableType()

Foreign Function Interface (dart:ffi)

  • Breaking Change: Changed Pointer.asFunction() and DynamicLibrary.lookupFunction() to extension methods. Invoking them dynamically previously already threw an exception, so the runtime behavior stays the same. However, the extension methods are only visible if dart:ffi is imported directly. This breaks code where dart:ffi is not directly imported. To fix, add:

    import 'dart:ffi';


Dart Dev Compiler (DDC)

We fixed several inconsistencies between DDC and Dart2JS so that users less frequently encounter code that is accepted by one compiler but then fails in the other.

  • Breaking Change: Deleted the legacy (analyzer based) version of DDC. For additional details see the announcement.

    • The --kernel option is now ignored and defaults to true. There is no longer any way to invoke the legacy (analyzer based) version of DDC.

    • Command line arguments that were only used for the legacy DDC have been removed.

    • The pre-compiled dart_sdk.js artifacts generated by legacy DDC have been deleted from dart-sdk/lib/dev_compiler in favor of the versions located at dart-sdk/lib/dev_compiler/kernel.

  • Breaking Change: Functions passed to JavaScript using the recommended package:js interop specification must now be wrapped with a call to allowInterop. This behavior was always enforced by Dart2JS, but was not enforced consistently by DDC. It is now enforced by both.

  • Breaking Change: Constructors in @JS() classes must be marked with external. Previously the external could be omitted in some cases with DDC but doing so would cause incorrect behavior with Dart2JS.

  • JS interop classes with an index operator are now static errors.

  • All remaining support from the dart:mirrors library has been removed. Use of this library on the web has been unsupported and prevented by the Dart build systems since Dart v2.0.0. All known exception cases have been cleaned up. This change makes DDC and Dart2JS now behave consistently.

    The library can still be imported on web apps, but all APIs throw. In a future breaking change release, imports to this library will likely become a compile-time error.


A new representation of runtime types is enabled by default.

This change is part of a long term goal of making runtime checks cheaper and more flexible for upcoming changes in the language. The new representation disentangles how types and classes are represented and makes types first-class to the compiler. This makes it possible to do certain kind of optimizations on type checks that were not possible before and will enable us to model non-nullable types in the near future.

This change should not affect the semantics of your application, but it has some relatively small visible effects that we want to highlight:

  • Types are now canonicalized, this fixes a long standing bug that Types could not be used in switch cases (issue 17207).

  • Code-size changes may be visible, but the difference is small overall. It is more visible on smaller apps because the new implementation includes more helper methods. On large apps we have even seen an overall code-size reduction.

  • Certain checks are a lot faster. This is less noticeable if you are compiling apps with -O3 where checks are omitted altogether. Even with -O3, the performance of some is checks used by your app may improve.

  • When using -O3 and -O4 incorrect type annotations could surface as errors. The old type representation was accidentally lenient on some invalid type annotations. We have only encountered this issue on programs that were not tested properly at the js-interop program boundary.

  • Type.toString() has a small change that is rarely visible. For a long time, Dart2JS has had support to erase unused type variables. Today, when Dart2JS is given --lax-runtime-type-to-string (currently included in -O2, -O3, and -O4) and it decides to erase the type variable of a class Foo<T>, then it compiles expressions like foo.runtimeType.toString() to print Foo. With the new representation, this will show Foo<erased> instead. This change may be visible in error messages produced by type checks involving erased types.

Because types and classes are represented separately, we will likely reevaluate restrictions of deferred libraries in the near future. For example, we could support referring to deferred types because types can be downloaded while classes are not.

In the unlikely case you run into any issues, please file a bug so we can investigate. You can temporarily force the old type representation by passing --use-old-rti to Dart2JS if necessary, but our goal is to delete the old type representation soon.

In addition, we fixed some inconsistencies between Dart2JS and DDC:

  • JS interop classes with an index operator are now static errors instead of causing invalid code in Dart2JS.

  • Breaking Change: The subtyping rule for generic functions is now more forgiving. Corresponding type parameter bounds now only need to be mutual subtypes rather than structurally equal up to renaming of bound type variables and equating all top types.

  • Breaking Change: Types are now normalized. See normalization for the full specification. Types will now be printed in their normal form, and mutual subtypes with the same normal form will now be considered equal.

  • Breaking Change: Constructors in @JS() classes must be marked with external. Previously, the external could be omitted for unused constructors. Omitting external for a constructor which is used would cause incorrect behavior at runtime, now omitting it on any constructor is a static error.

Other dart2js changes:

  • Breaking Change: The --package-root flag, which was hidden and disabled in Dart 2.0.0, has been completely removed. Passing this flag will now cause dart2js to fail.


Updated the Linter to 0.1.114, which includes:

  • Fixed avoid_shadowing_type_parameters to support extensions and mixins.
  • Updated non_constant_identifier_names to allow named constructors made up of only underscores (_).
  • Updated avoid_unused_constructor_parameters to ignore unused params named in all underscores (_).


  • Removed support for the deprecated analysis options file name .analysis_options.


  • Added pub outdated command which lists outdated package dependencies, and gives advice on how to upgrade.

  • pub get and pub upgrade now fetch version information about hosted dependencies in parallel, improving the time package resolution performance.

  • pub get and pub upgrade no longer precompile executables from dependencies by default. Instead they are precompiled on first pub run. Use pub get --precompile to get the previous behavior.

  • Fixed missing retries of DNS failures during pub get.

  • If code contains imports for packages not listed in the package's pubspec.yaml then pub publish will reject the package.

  • pub publish no longer requires the presence of a homepage field, if the repository field is provided.

  • pub publish warns if non-pre-release packages depends on pre-release packages or pre-release Dart SDKs.

  • Relative paths in pubspec.lock now use / also on Windows to make the file sharable between machines.

  • Fixed language version in .dart_tool/package_config.json for packages without an explicit SDK constraint. Pub now writes an empty language version where before the language version of the current SDK would be used.

  • %LOCALAPPDATA% is now preferred over %APPDATA% when creating a pub cache directory on Windows. %LOCALAPPDATA% is not copied when users roam between devices.

  • pub publish warns if LICENSE and README.md files are not called those exact names.

  • pub repair cache downloads hosted packages in parallel.

2.7.2 - 2020-03-23

This is a patch release that addresses a vulnerability in dart:html NodeValidator related to DOM clobbering of previousSibling. See the vulnerability advisory for more details. Thanks to Vincenzo di Cicco for finding and reporting this issue.

This release also improves compatibility with ARMv8 processors (issue 40001) and dart:io stability (issue 40589).

2.7.1 - 2020-01-23

This is a patch release that improves dart2js compile-time (issue 40217).

Breaking Change: The Dart SDK for macOS is now only available for x64 (issue 39810).

2.7.0 - 2019-12-11

Extension methods -- which we shipped in preview in 2.6.0 -- are no longer in preview, and are now officially supported as of 2.7.0. Learn more about them here:



  • Breaking Change: Static extension members are accessible when imported with a prefix (issue 671). In the extension method preview launch, importing a library with a prefix hid all extension members in addition to hiding the extension name, thereby making them inaccessible in the importing library except via the explicit override syntax. Based on user feedback, we have changed this to make extensions methods accessible even when imported with a prefix.

      // "thing.dart"
      class Thing {
      extension Show on Thing {
        void show() {
          print("This is a thing");
     // "client.dart"
     import "thing.dart" as p;
     void test() {
       p.Thing().show(); // Previously an error, now resolves to Show.show

Core libraries


  • Breaking change: Added IOOverrides.serverSocketBind to aid in writing tests that wish to mock ServerSocket.bind.


  • Added new constructors, .sublistView(TypedData, [start, end]) to all TypedData classes. The constructor makes it easier, and less error-prone, to create a view of (a slice of) another TypedData object.

Dart VM

  • New fields added to existing instances by a reload will now be initialized lazily, as if the field was a late field. This makes the initialization order program-defined, whereas previously it was undefined.



The Linter was updated to 0.1.104, which includes:

  • updated unnecessary_overrides to allow overrides when annotations (besides @override are specified)
  • updated file_names to allow names w/ leading _'s (and improved performance)
  • new lint: unnecessary_final


  • pub get generates .dart_tool/package_config.json in addition to .packages to support language versioning.

  • pub publish now warns about the old flutter plugin registration format.

  • pub publish now warns about the author field in pubspec.yaml being. obsolete.

  • Show a proper error message when git is not installed.

2.6.1 - 2019-11-11

This is a patch release that reduces dart2js memory usage (issue 27883), improves stability on arm64 (issue 39090) and updates the Dart FFI documentation.

2.6.0 - 2019-11-05


  • [IN PREVIEW] Static extension members: A new language feature allowing specially declared static functions to be invoked like instance members on expressions of appropriate static types is available in preview.

    Static extension members are declared using a new extension declaration. Example:

    extension MyFancyList<T> on List<T> {
      /// Whether this list has an even length.
      bool get isLengthEven => this.length.isEven;
      /// Whether this list has an odd length.
      bool get isLengthOdd => !isLengthEven;
      /// List of values computed for each pairs of adjacent elements.
      /// The result always has one element less than this list,
      /// if this list has any elements.
      List<R> combinePairs<R>(R Function(T, T) combine) =>
          [for (int i = 1; i < this.length; i++)
              combine(this[i - 1], this[i])];

    Extension declarations cannot declare instance fields or constructors. Extension members can be invoked explicitly, MyFancyList(intList).isLengthEven), or implicitly, intList.isLengthEven, where the latter is recognized by intList matching the List<T> “on” type of the declaration. An extension member cannot be called implicitly on an expression whose static type has a member with the same base-name. In that case, the interface member takes precedence. If multiple extension members apply to the same implicit invocation, the most specific one is used, if there is one such.

    Extensions can be declared on any type, not just interface types.

    extension IntCounter on int {
      /// The numbers from this number to, but not including, [end].
      Iterable<int> to(int end) sync* {
        int step = end < this ? -1 : 1;
        for (int i = this; i != end; i += step) yield i;
    extension CurryFunction<R, S, T> on R Function(S, T) {
      /// Curry a binary function with its first argument.
      R Function(T) curry(S first) => (T second) => this(first, second);
  • Breaking change #37985: Inference is changed when using Null values in a FutureOr context. Namely, constraints of the forms similar to Null <: FutureOr<T> now yield Null as the solution for T. For example, the following code will now print “Null”, and it was printing “dynamic” before (note that the anonymous closure () {} in the example has Null as its return type):

    import 'dart:async';
    void foo<T>(FutureOr<T> Function() f) { print(T); }
    main() { foo(() {}); }

Core libraries

  • Default values of parameters of abstract methods are no longer available via dart:mirrors.


  • Added optional parent parameter to TimelineTask constructor to allow for linking of asynchronous timeline events in the DevTools timeline view.


  • Added enableTimelineLogging property to HttpClient which, when enabled, will post HTTP connection and request information to the developer timeline for all HttpClient instances.

Dart VM

Foreign Function Interface (dart:ffi)

  • Breaking change: The API now makes use of static extension members. Static extension members enable the dart:ffi API to be more precise with types, and provide convenient access to memory through extension getters and setters. The extension members on Pointer provide .value and .value = for accessing the value in native memory and [] and []= for indexed access. The method asExternalTypedData has been replaced with asTypedList extension methods. And finally, Structs do no longer have a type argument and are accessed using the extension member .ref on Pointer. These changes makes the code using dart:ffi much more concise.
  • Breaking change: The memory management has been removed (Pointer.allocate and Pointer.free). Instead, memory management is available in package:ffi.
  • Breaking change: Pointer.offsetBy was removed, use cast and elementAt instead.
  • Faster memory load and stores.
  • The dartanalyzer (commandline and IDEs) now reports dart:ffi static errors.
  • Callbacks are now supported in AOT (ahead-of-time) compiled code.

Dart for the Web

Dart Dev Compiler (DDC)

  • Kernel DDC will no longer accept non-dill files as summary inputs.
  • Removed support for the deprecated web extension.



The Linter was updated to 0.1.101, which includes:

  • fixed diagnostic_describe_all_properties to flag properties in Diagnosticables with no debug methods defined
  • fixed noSuchMethod exception in camel_case_extensions when analyzing unnamed extensions
  • fixed avoid_print to catch tear-off usage
  • new lint: avoid_web_libraries_in_flutter (experimental)
  • (internal) prepare unnecessary_lambdas for coming MethodInvocation vs. FunctionExpressionInvocation changes

2.5.2 - 2019-10-08

This is a patch release with properly signed binaries required for macOS Catalina (Issue 38765).

2.5.1 - 2019-09-27

This is a patch release that prevents type inference failures in the analyzer (Issue 38365).

2.5.0 - 2019-09-10


The set of operations allowed in constant expressions has been expanded as described in the constant update proposal. The control flow and spread collection features shipped in Dart 2.3 are now also supported in constants as described in the specification here.

Specifically, it is now valid to use the following operations in constant expressions under the appropriate conditions:

  • Casts (e as T) and type tests (e is T).
  • Comparisons to null, even for types which override the == operator.
  • The &, |, and ^ binary operators on booleans.
  • The spread operators (... and ...?).
  • An if element in a collection literal.
// Example: these are now valid constants.
const Object i = 3;
const list = [i as int];
const set = {if (list is List<int>) ...list};
const map = {if (i is int) i : "int"};

In addition, the semantics of constant evaluation has been changed as follows:

  • The && operator only evaluates its second operand if the first evaluates to true.
  • The || operator only evaluates its second operand if the first evaluates to false.
  • The ?? operator only evaluates its second operand if the first evaluates to null.
  • The conditional operator (e ? e1 : e2) only evaluates one of the two branches, depending on the value of the first operand.
// Example: x is now a valid constant definition.
const String s = null;
const int x = (s == null) ? 0 : s.length;

Core libraries

  • Breaking change #36900: The following methods and properties across various core libraries, which used to declare a return type of List<int>, were updated to declare a return type of Uint8List:

    • BytesBuilder.takeBytes()
    • BytesBuilder.toBytes()
    • Datagram.data
    • File.readAsBytes() (Future<Uint8List>)
    • File.readAsBytesSync()
    • InternetAddress.rawAddress
    • RandomAccessFile.read() (Future<Uint8List>)
    • RandomAccessFile.readSync()
    • RawSocket.read()
    • Utf8Codec.encode() (and Utf8Encoder.convert())

    In addition, the following classes were updated to implement Stream<Uint8List> rather than Stream<List<int>>:

    • HttpRequest
    • Socket

    Possible errors and how to fix them

    • The argument type ‘Utf8Decoder’ can't be assigned to the parameter type ‘StreamTransformer<Uint8List, dynamic>’

      type ‘Utf8Decoder’ is not a subtype of type ‘StreamTransformer’ of ‘streamTransformer’"

      You can fix these call sites by updating your code to use StreamTransformer.bind() instead of Stream.transform(), like so:

      Before: stream.transform(utf8.decoder) After: utf8.decoder.bind(stream)

    • The argument type ‘IOSink’ can't be assigned to the parameter type ‘StreamConsumer’

      type ‘_IOSinkImpl’ is not a subtype of type ‘StreamConsumer’ of ‘streamConsumer’

      You can fix these call sites by casting your stream instance to a Stream<List<int>> before calling .pipe() on the stream, like so:

      Before: stream.pipe(consumer) After: stream.cast<List<int>>().pipe(consumer)

    Finally, the following typed lists were updated to have their sublist() methods declare a return type that is the same as the source list:

    • Int8List.sublist()Int8List
    • Int16List.sublist()Int16List
    • Int32List.sublist()Int32List
    • Int64List.sublist()Int64List
    • Int32x4List.sublist()Int32x4List
    • Float32List.sublist()Float32List
    • Float64List.sublist()Float64List
    • Float32x4List.sublist()Float32x4List
    • Float64x2List.sublist()Float64x2List
    • Uint8List.sublist()Uint8List
    • Uint8ClampedList.sublist()Uint8ClampedList
    • Uint16List.sublist()Uint16List
    • Uint32List.sublist()Uint32List
    • Uint64List.sublist()Uint64List


  • Add value and error constructors on Stream to allow easily creating single-value or single-error streams.


  • Update Uri class to support RFC6874: “%25” or “%” can be appended to the end of a valid IPv6 representing a Zone Identifier. A valid zone ID consists of unreversed character or Percent encoded octet, which was defined in RFC3986. IPv6addrz = IPv6address “%25” ZoneID


  • Breaking change #37192: The Cookie class‘s constructor’s name and value optional positional parameters are now mandatory. The signature changes from:

    Cookie([String name, String value])


    Cookie(String name, String value)

    However, it has not been possible to set name and value to null since Dart 1.3.0 (2014) where a bug made it impossible. Any code not using both parameters or setting any to null would necessarily get a noSuchMethod exception at runtime. This change catches such erroneous uses at compile time. Since code could not previously correctly omit the parameters, this is not really a breaking change.

  • Breaking change #37192: The Cookie class‘s name and value setters now validates that the strings are made from the allowed character set and are not null. The constructor already made these checks and this fixes the loophole where the setters didn’t also validate.

Dart VM



  • Clean-up invalid git repositories in cache when fetching from git.
  • Breaking change #36765: Packages published to pub.dev can no longer contain git dependencies. These packages will be rejected by the server.


The Linter was updated to 0.1.96, which includes:

  • fixed false positives in unnecessary_parens
  • various changes to migrate to preferred analyzer APIs
  • rule test fixes


Dartdoc was updated to 0.28.4; this version includes several fixes and is based on a newer version of the analyzer package.

2.4.1 - 2019-08-07

This is a patch release that fixes a performance regression in JIT mode, as well as a potential crash of our AOT compiler.

Dart VM

  • Fixed a performance regression where usage of Int32List could trigger repeated deoptimizations in JIT mode (Issue 37551).

  • Fixed a bug where usage of a static getter with name length could cause a crash in our AOT compiler (Issue 35121).

Dart Dev Compiler (DDC)

Callbacks passed to JS and wrapped with allowInterop or allowInteropCaptureThis are now strict about argument counts and argument types. This may mean that tests which were previously passing and relying on loose argument checking (too many or too few arguments, or arguments with too specific types like List<Something> instead of List<dynamic>) may start failing. This changes makes DDC behave more like dart2js with the default flags.

2.4.0 - 2019-06-27

Core libraries


  • TransferableTypedData class was added to facilitate faster cross-isolate communication of Uint8List data.

  • Breaking change: Isolate.resolvePackageUri will always throw an UnsupportedError when compiled with dart2js or DDC. This was the only remaining API in dart:isolate that didn't automatically throw since we dropped support for this library in Dart 2.0.0. Note that the API already throws in dart2js if the API is used directly without manually setting up a defaultPackagesBase hook.


  • Exposed result, errorCode and errorDetail getters in ServiceExtensionResponse to allow for better debugging of VM service extension RPC results.


  • Fixed Cookie class interoperability with certain websites by allowing the cookie values to be the empty string (Issue 35804) and not stripping double quotes from the value (Issue 33327) in accordance with RFC 6265.

  • #36971: The HttpClientResponse interface has been extended with the addition of a new compressionState getter, which specifies whether the body of a response was compressed when it was received and whether it has been automatically uncompressed via HttpClient.autoUncompress.

    As part of this change, a corresponding new enum was added to dart:io: HttpClientResponseCompressionState.

    This is a breaking change for those implementing the HttpClientResponse interface as subclasses will need to implement the new getter.


  • Breaking change #36382: The await for allowed null as a stream due to a bug in StreamIterator class. This bug has now been fixed.


  • #36171: The RegExp interface has been extended with two new constructor named parameters:

    • unicode: (bool, default: false), for Unicode patterns
    • dotAll: (bool, default: false), to change the matching behavior of ‘.’ to also match line terminating characters.

    Appropriate properties for these named parameters have also been added so their use can be detected after construction.

    In addition, RegExp methods that originally returned Match objects now return a more specific subtype, RegExpMatch, which adds two features:

    • Iterable<String> groupNames, a property that contains the names of all named capture groups
    • String namedGroup(String name), a method that retrieves the match for the given named capture group

    This is a breaking change for implementers of the RegExp interface. Subclasses will need to add the new properties and may have to update the return types on overridden methods.


  • Breaking change #35097: Covariance of type variables used in super-interfaces is now enforced. For example, the following code was previously accepted and will now be rejected:
class A<X> {};
class B<X> extends A<void Function(X)> {};
  • The identifier async can now be used in asynchronous and generator functions.

Dart for the Web

Dart Dev Compiler (DDC)

  • Improve NoSuchMethod errors for failing dynamic calls. Now they include specific information about the nature of the error such as:
    • Attempting to call a null value.
    • Calling an object instance with a null call() method.
    • Passing too few or too many arguments.
    • Passing incorrect named arguments.
    • Passing too few or too many type arguments.
    • Passing type arguments to a non-generic method.



The Linter was updated to 0.1.91, which includes the following changes:

  • Fixed missed cases in prefer_const_constructors
  • Fixed prefer_initializing_formals to no longer suggest API breaking changes
  • Updated omit_local_variable_types to allow explicit dynamics
  • Fixed null-reference in unrelated_type_equality_checks
  • New lint: unsafe_html
  • Broadened prefer_null_aware_operators to work beyond local variables.
  • Added prefer_if_null_operators.
  • Fixed prefer_contains false positives.
  • Fixed unnecessary_parenthesis false positives.
  • Fixed prefer_asserts_in_initializer_lists false positives
  • Fixed curly_braces_in_flow_control_structures to handle more cases
  • New lint: prefer_double_quotes
  • New lint: sort_child_properties_last
  • Fixed type_annotate_public_apis false positive for static const initializers


  • pub publish will no longer warn about missing dependencies for import statements in example/.
  • OAuth2 authentication will explicitly ask for the openid scope.

2.3.2 - 2019-06-11

This is a patch version release with a security improvement.

Security vulnerability

  • Security improvement: On Linux and Android, starting a process with Process.run, Process.runSync, or Process.start would first search the current directory before searching PATH (Issue 37101). This behavior effectively put the current working directory in the front of PATH, even if it wasn‘t in the PATH. This release changes that behavior to only searching the directories in the PATH environment variable. Operating systems other than Linux and Android didn’t have this behavior and aren't affected by this vulnerability.

    This vulnerability could result in execution of untrusted code if a command without a slash in its name was run inside an untrusted directory containing an executable file with that name:

    Process.run("ls", workingDirectory: "/untrusted/directory")

    This would attempt to run /untrusted/directory/ls if it existed, even though it is not in the PATH. It was always safe to instead use an absolute path or a path containing a slash.

    This vulnerability was introduced in Dart 2.0.0.

2.3.1 - 2019-05-21

This is a patch version release with bug fixes.



  • Fixed a bug that caused the compiler to crash when it compiled UI-as-code features within fields (Issue 36864).

2.3.0 - 2019-05-08

The focus in this release is on the new “UI-as-code” language features which make collections more expressive and declarative.


Flutter is growing rapidly, which means many Dart users are building UI in code out of big deeply-nested expressions. Our goal with 2.3.0 was to make that kind of code easier to write and maintain. Collection literals are a large component, so we focused on three features to make collections more powerful. We'll use list literals in the examples below, but these features also work in map and set literals.


Placing ... before an expression inside a collection literal unpacks the result of the expression and inserts its elements directly inside the new collection. Where before you had to write something like this:

  child: ListView(children: [

Now you can write this:

  child: ListView(children: [

If you know the expression might evaluate to null and you want to treat that as equivalent to zero elements, you can use the null-aware spread ...?.

Collection if

Sometimes you might want to include one or more elements in a collection only under certain conditions. If you're lucky, you can use a ?: operator to selectively swap out a single element, but if you want to exchange more than one or omit elements, you are forced to write imperative code like this:

Widget build(BuildContext context) {
  var children = [
    IconButton(icon: Icon(Icons.menu)),
    Expanded(child: title)

  if (isAndroid) {
    children.add(IconButton(icon: Icon(Icons.search)));

  return Row(children: children);

We now allow if inside collection literals to conditionally omit or (with else) swap out an element:

Widget build(BuildContext context) {
  return Row(
    children: [
      IconButton(icon: Icon(Icons.menu)),
      Expanded(child: title),
      if (isAndroid)
        IconButton(icon: Icon(Icons.search)),

Unlike the existing ?: operator, a collection if can be composed with spreads to conditionally include or omit multiple items:

Widget build(BuildContext context) {
  return Row(
    children: [
      IconButton(icon: Icon(Icons.menu)),
      if (isAndroid) ...[
        Expanded(child: title),
        IconButton(icon: Icon(Icons.search)),

Collection for

In many cases, the higher-order methods on Iterable give you a declarative way to modify a collection in the context of a single expression. But some operations, especially involving both transforming and filtering, can be cumbersome to express in a functional style.

To solve this problem, you can use for inside a collection literal. Each iteration of the loop produces an element which is then inserted in the resulting collection. Consider the following code:

var command = [
  ...fileSystemRoots.map((root) => "--filesystem-root=$root"),
      .where((entryPoint) => fileExists("lib/$entryPoint.json"))
      .map((entryPoint) => "lib/$entryPoint"),

With a collection for, the code becomes simpler:

var command = [
  for (var root in fileSystemRoots) "--filesystem-root=$root",
  for (var entryPoint in entryPoints)
    if (fileExists("lib/$entryPoint.json")) "lib/$entryPoint",

As you can see, all three of these features can be freely composed. For full details of the changes, see the official proposal.

Note: These features are not currently supported in const collection literals. In a future release, we intend to relax this restriction and allow spread and collection if inside const collections.

Core library changes


  • Added debugName property to Isolate.
  • Added debugName optional parameter to Isolate.spawn and Isolate.spawnUri.


  • RegExp patterns can now use lookbehind assertions.
  • RegExp patterns can now use named capture groups and named backreferences. Currently, named group matches can only be retrieved in Dart either by the implicit index of the named group or by downcasting the returned Match object to the type RegExpMatch. The RegExpMatch interface contains methods for retrieving the available group names and retrieving a match by group name.

Dart VM

  • The VM service now requires an authentication code by default. This behavior can be disabled by providing the --disable-service-auth-codes flag.

  • Support for deprecated flags ‘-c’ and ‘--checked’ has been removed.

Dart for the Web


A binary format was added to dump-info. The old JSON format is still available and provided by default, but we are starting to deprecate it. The new binary format is more compact and cheaper to generate. On some large apps we tested, it was 4x faster to serialize and used 6x less memory.

To use the binary format today, use --dump-info=binary, instead of --dump-info.

What to expect next?

  • The visualizer tool will not be updated to support the new binary format, but you can find several command-line tools at package:dart2js_info that provide similar features to those in the visualizer.

  • The command-line tools in package:dart2js_info also work with the old JSON format, so you can start using them even before you enable the new format.

  • In a future release --dump-info will default to --dump-info=binary. At that point, there will be an option to fallback to the JSON format, but the visualizer tool will be deprecated.

  • A release after that, the JSON format will no longer be available from dart2js, but may be available from a command-line tool in package:dart2js_info.



  • Tweak set literal formatting to follow other collection literals.
  • Add support for “UI as code” features.
  • Properly format trailing commas in assertions.
  • Improve indentation of adjacent strings in argument lists.


The Linter was updated to 0.1.86, which includes the following changes:

  • Added the following lints: prefer_inlined_adds, prefer_for_elements_to_map_fromIterable, prefer_if_elements_to_conditional_expressions, diagnostic_describe_all_properties.
  • Updated file_names to skip prefixed-extension Dart files (.css.dart, .g.dart, etc.).
  • Fixed false positives in unnecessary_parenthesis.


  • Added a CHANGELOG validator that complains if you pub publish without mentioning the current version.
  • Removed validation of library names when doing pub publish.
  • Added support for pub global activateing package from a custom pub URL.
  • Added subcommand: pub logout. Logs you out of the current session.

Dart native

Initial support for compiling Dart apps to native machine code has been added. Two new tools have been added to the bin folder of the Dart SDK:

  • dart2aot: AOT (ahead-of-time) compiles a Dart program to native machine code. The tool is supported on Windows, macOS, and Linux.

  • dartaotruntime: A small runtime used for executing an AOT compiled program.

2.2.0 - 2019-02-26


Sets now have a literal syntax like lists and maps do:

var set = {1, 2, 3};

Using curly braces makes empty sets ambiguous with maps:

var collection = {}; // Empty set or map?

To avoid breaking existing code, an ambiguous literal is treated as a map. To create an empty set, you can rely on either a surrounding context type or an explicit type argument:

// Variable type forces this to be a set:
Set<int> set = {};

// A single type argument means this must be a set:
var set2 = <int>{};

Set literals are released on all platforms. The set-literals experiment flag has been disabled.



  • The DEPRECATED_MEMBER_USE hint was split into two hints:

    • DEPRECATED_MEMBER_USE reports on usage of @deprecated members declared in a different package.
    • DEPRECATED_MEMBER_USE_FROM_SAME_PACKAGE reports on usage of @deprecated members declared in the same package.


Upgraded the linter to 0.1.82 which adds the following improvements:

  • Added provide_deprecation_message, and use_full_hex_values_for_flutter_colors, prefer_null_aware_operators.
  • Fixed prefer_const_declarations set literal false-positives.
  • Updated prefer_collection_literals to support set literals.
  • Updated unnecessary_parenthesis play nicer with cascades.
  • Removed deprecated lints from the “all options” sample.
  • Stopped registering “default lints”.
  • Fixed hash_and_equals to respect hashCode fields.

Other libraries


  • Breaking change: The klass getter on the InstanceConstant class in the Kernel AST API has been renamed to classNode for consistency.

  • Breaking change: Updated Link implementation to utilize true symbolic links instead of junctions on Windows. Existing junctions will continue to work with the new Link implementation, but all new links will create symbolic links.

    To create a symbolic link, Dart must be run with administrative privileges or Developer Mode must be enabled, otherwise a FileSystemException will be raised with errno set to ERROR_PRIVILEGE_NOT_HELD (Issue 33966).

2.1.1 - 2019-02-18

This is a patch version release. Again, the team's focus was mostly on improving performance and stability after the large changes in Dart 2.0.0. In particular, dart2js now always uses the “fast startup” emitter and the old emitter has been removed.

There are a couple of very minor breaking changes:

  • In dart:io, adding to a closed IOSink now throws a StateError.

  • On the Dart VM, a soundness hole when using dart:mirrors to reflectively invoke a method in an incorrect way that violates its static types has been fixed (Issue 35611).


This release has no language changes.

Core library


  • Made DateTime.parse() also recognize , as a valid decimal separator when parsing from a string (Issue 35576).


  • Added methods Element.removeAttribute, Element.removeAttributeNS, Element.hasAttribute and Element.hasAttributeNS. (Issue 35655).

  • Improved dart2js compilation of element.attributes.remove(name) to generate element.removeAttribute(name), so that there is no performance reason to migrate to the above methods.

  • Fixed a number of dart:html bugs:

    • Fixed HTML API's with callback typedef to correctly convert Dart functions to JS functions (Issue 35484).
    • HttpStatus constants exposed in dart:html (Issue 34318).
    • Expose DomName ondblclick and dblclickEvent for Angular analyzer.
    • Fixed removeAll on classes; elements parameter should be Iterable<Object> to match Set's removeAll not Iterable<E> (Issue 30278).
    • Fixed a number of methods on DataTransferItem, Entry, FileEntry and DirectoryEntry which previously returned NativeJavaScriptObject. This fixes handling drag/drop of files/directories (Issue 35510).
    • Added ability to allow local file access from Chrome browser in ddb.


  • Breaking Change: Adding to a closed IOSink now throws a StateError.
  • Added ability to get and set low level socket options.

Dart VM

In previous releases it was possible to violate static types using dart:mirrors. This code would run without any TypeErrors and print “impossible” output:

import 'dart:mirrors';

class A {
  void method(int v) {
    if (v != null && v is! int) {
      print("This should be impossible: expected null or int got ${v}");

void main() {
  final obj = A();
  reflect(obj).invoke(#method, ['not-an-number']);

This bug is fixed now. Only code that already violates static typing will break. See Issue 35611 for more details.

Dart for the Web


  • The old “full emitter” back-end is removed and dart2js always uses the “fast startup” back-end. The generated fast startup code is optimized to load faster, even though it can be slightly larger. The --fast-startup and --no-fast-startup are allowed but ignored. They will be removed in a future version.

  • We fixed a bug in how deferred constructor calls were incorrectly not marked as deferred. The old behavior didn't cause breakages, but was imprecise and pushed more code to the main output unit.

  • A new deferred split algorithm implementation was added.

    This implementation fixes a soundness bug and addresses performance issues of the previous implementation, because of that it can have a visible impact on apps. In particular:

    • We fixed a performance issue which was introduced when we migrated to the common front-end. On large apps, the fix can cut 2/3 of the time spent on this task.

    • We fixed a bug in how inferred types were categorized (Issue 35311). The old behavior was unsound and could produce broken programs. The fix may cause more code to be pulled into the main output unit.

      This shows up frequently when returning deferred values from closures since the closure's inferred return type is the deferred type. For example, if you have:

      () async {
        await deferred_prefix.loadLibrary();
        return new deferred_prefix.Foo();

      The closure's return type is Future<Foo>. The old implementation defers Foo, and incorrectly makes the return type Future<dynamic>. This may break in places where the correct type is expected.

      The new implementation will not defer Foo, and will place it in the main output unit. If your intent is to defer it, then you need to ensure the return type is not inferred to be Foo. For example, you can do so by changing the code to a named closure with a declared type, or by ensuring that the return expression has the type you want, like:

      () async {
        await deferred_prefix.loadLibrary();
        return new deferred_prefix.Foo() as dynamic;

      Because the new implementation might require you to inspect and fix your app, we exposed two temporary flags:

    • The --report-invalid-deferred-types causes dart2js to run both the old and new algorithms and report any cases where an invalid type was detected.

    • The --new-deferred-split flag enables this new algorithm.

  • The --categories=* flag is being replaced. --categories=all was only used for testing and it is no longer supported. --categories=Server continues to work at this time but it is deprecated, please use --server-mode instead.

  • The --library-root flag was replaced by --libraries-spec. This flag is rarely used by developers invoking dart2js directly. It's important for integrating dart2js with build systems. See --help for more details on the new flag.



  • Support for declarations-casts has been removed and the implicit-casts option now has the combined semantics of both options. This means that users that disable implicit-casts might now see errors that were not previously being reported.

  • New hints added:

    • NON_CONST_CALL_TO_LITERAL_CONSTRUCTOR and NON_CONST_CALL_TO_LITERAL_CONSTRUCTOR_USING_NEW inform you when a @literal const constructor is called in a non-const context (or with new).
    • INVALID_LITERAL_ANNOTATION reports when something other than a const constructor is annotated with @literal.
    • SUBTYPE_OF_SEALED_CLASS reports when any class or mixin subclasses (extends, implements, mixes in, or constrains to) a @sealed class, and the two are declared in different packages.
    • MIXIN_ON_SEALED_CLASS reports when a @sealed class is used as a superclass constraint of a mixin.


Default styles now work much better on mobile. Simple browsing and searching of API docs now work in many cases.

Upgraded the linter to 0.1.78 which adds the following improvements:

  • Added prefer_final_in_for_each, unnecessary_await_in_return, use_function_type_syntax_for_parameters, avoid_returning_null_for_future, and avoid_shadowing_type_parameters.
  • Updated invariant_booleans status to experimental.
  • Fixed type_annotate_public_apis false positives on local functions.
  • Fixed avoid_shadowing_type_parameters to report shadowed type parameters in generic typedefs.
  • Fixed use_setters_to_change_properties to not wrongly lint overriding methods.
  • Fixed cascade_invocations to not lint awaited targets.
  • Fixed prefer_conditional_assignment false positives.
  • Fixed join_return_with_assignment false positives.
  • Fixed cascade_invocations false positives.
  • Deprecated prefer_bool_in_asserts as it is redundant in Dart 2.

2.1.0 - 2018-11-15

This is a minor version release. The team's focus was mostly on improving performance and stability after the large changes in Dart 2.0.0. Notable changes:

  • We've introduced a dedicated syntax for declaring a mixin. Instead of the class keyword, it uses mixin:

    mixin SetMixin<E> implements Set<E> {

    The new syntax also enables super calls inside mixins.

  • Integer literals now work in double contexts. When passing a literal number to a function that expects a double, you no longer need an explicit .0 at the end of the number. In releases before 2.1, you need code like this when setting a double like fontSize:

    TextStyle(fontSize: 18.0)

    Now you can remove the .0:

    TextStyle(fontSize: 18)

    In releases before 2.1, fontSize : 18 causes a static error. This was a common mistake and source of friction.

  • Breaking change: A number of static errors that should have been detected and reported were not supported in 2.0.0. These are reported now, which means existing incorrect code may show new errors.

  • dart:core now exports Future and Stream. You no longer need to import dart:async to use those very common types.


  • Introduced a new syntax for mixin declarations.

    mixin SetMixin<E> implements Set<E> {

    Most classes that are intended to be used as mixins are intended to only be used as mixins. The library author doesn't want users to be able to construct or subclass the class. The new syntax makes that intent clear and enforces it in the type system. It is an error to extend or construct a type declared using mixin. (You can implement it since mixins expose an implicit interface.)

    Over time, we expect most mixin declarations to use the new syntax. However, if you have a “mixin” class where users are extending or constructing it, note that moving it to the new syntax is a breaking API change since it prevents users from doing that. If you have a type like this that is a mixin as well as being a concrete class and/or superclass, then the existing syntax is what you want.

    If you need to use a super inside a mixin, the new syntax is required. This was previously only allowed with the experimental --supermixins flag because it has some complex interactions with the type system. The new syntax addresses those issues and lets you use super calls by declaring the superclass constraint your mixin requires:

    class Superclass {
      superclassMethod() {
        print("in superclass");
    mixin SomeMixin on Superclass {
      mixinMethod() {
        // This is OK:
    class GoodSub extends Superclass with SomeMixin {}
    class BadSub extends Object with SomeMixin {}
    // Error: Since the super() call in mixinMethod() can't find a
    // superclassMethod() to call, this is prohibited.

    Even if you don't need to use super calls, the new mixin syntax is good because it clearly expresses that you intend the type to be mixed in.

  • Allow integer literals to be used in double contexts. An integer literal used in a place where a double is required is now interpreted as a double value. The numerical value of the literal needs to be precisely representable as a double value.

  • Integer literals compiled to JavaScript are now allowed to have any value that can be exactly represented as a JavaScript Number. They were previously limited to such numbers that were also representable as signed 64-bit integers.

(Breaking) A number of static errors that should have been detected and reported were not supported in 2.0.0. These are reported now, which means existing incorrect code may show new errors:

  • Setters with the same name as the enclosing class aren't allowed. (Issue 34225.) It is not allowed to have a class member with the same name as the enclosing class:

    class A {
      set A(int x) {}

    Dart 2.0.0 incorrectly allows this for setters (only). Dart 2.1.0 rejects it.

    To fix: This is unlikely to break anything, since it violates all style guides anyway.

  • Constant constructors cannot redirect to non-constant constructors. (Issue 34161.) It is not allowed to have a constant constructor that redirects to a non-constant constructor:

    class A {
      const A.foo() : this(); // Redirecting to A()
      A() {}

    Dart 2.0.0 incorrectly allows this. Dart 2.1.0 rejects it.

    To fix: Make the target of the redirection a properly const constructor.

  • Abstract methods may not unsoundly override a concrete method. (Issue 32014.) Concrete methods must be valid implementations of their interfaces:

    class A {
      num get thing => 2.0;
    abstract class B implements A {
      int get thing;
    class C extends A with B {}
    // 'thing' from 'A' is not a valid override of 'thing' from 'B'.
    main() {
      print(new C().thing.isEven); // Expects an int but gets a double.

    Dart 2.0.0 allows unsound overrides like the above in some cases. Dart 2.1.0 rejects them.

    To fix: Relax the type of the invalid override, or tighten the type of the overridden method.

  • Classes can't implement FutureOr. (Issue 33744.) Dart doesn't allow classes to implement the FutureOr type:

    class A implements FutureOr<Object> {}

    Dart 2.0.0 allows classes to implement FutureOr. Dart 2.1.0 does not.

    To fix: Don't do this.

  • Type arguments to generic typedefs must satisfy their bounds. (Issue 33308.) If a parameterized typedef specifies a bound, actual arguments must be checked against it:

    class A<X extends int> {}
    typedef F<Y extends int> = A<Y> Function();
    F<num> f = null;

    Dart 2.0.0 allows bounds violations like F<num> above. Dart 2.1.0 rejects them.

    To fix: Either remove the bound on the typedef parameter, or pass a valid argument to the typedef.

  • Constructor invocations must use valid syntax, even with optional new. (Issue 34403.) Type arguments to generic named constructors go after the class name, not the constructor name, even when used without an explicit new:

    class A<T> {
      A.foo() {}
    main() {
      A.foo<String>(); // Incorrect syntax, was accepted in 2.0.0.
      A<String>.foo(); // Correct syntax.

    Dart 2.0.0 accepts the incorrect syntax when the new keyword is left out. Dart 2.1.0 correctly rejects this code.

    To fix: Move the type argument to the correct position after the class name.

  • Instance members should shadow prefixes. (Issue 34498.) If the same name is used as an import prefix and as a class member name, then the class member name takes precedence in the class scope.

    import 'dart:core';
    import 'dart:core' as core;
    class A {
      core.List get core => null; // "core" refers to field, not prefix.

    Dart 2.0.0 incorrectly resolves the use of core in core.List to the prefix name. Dart 2.1.0 correctly resolves this to the field name.

    To fix: Change the prefix name to something which does not clash with the instance member.

  • Implicit type arguments in extends clauses must satisfy the class bounds. (Issue 34532.) Implicit type arguments for generic classes are computed if not passed explicitly, but when used in an extends clause they must be checked for validity:

    class Foo<T> {}
    class Bar<T extends Foo<T>> {}
    class Baz extends Bar {} // Should error because Bar completes to Bar<Foo>

    Dart 2.0.0 accepts the broken code above. Dart 2.1.0 rejects it.

    To fix: Provide explicit type arguments to the superclass that satisfy the bound for the superclass.

  • Mixins must correctly override their superclasses. (Issue 34235.) In some rare cases, combinations of uses of mixins could result in invalid overrides not being caught:

    class A {
      num get thing => 2.0;
    class M1 {
      int get thing => 2;
    class B = A with M1;
    class M2 {
      num get thing => 2.0;
    class C extends B with M2 {} // 'thing' from 'M2' not a valid override.
    main() {
      M1 a = new C();
      print(a.thing.isEven); // Expects an int but gets a double.

    Dart 2.0.0 accepts the above example. Dart 2.1.0 rejects it.

    To fix: Ensure that overriding methods are correct overrides of their superclasses, either by relaxing the superclass type, or tightening the subclass/mixin type.

Core libraries


  • Fixed a bug where calling stream.take(0).drain(value) would not correctly forward the value through the returned Future.
  • Added a StreamTransformer.fromBind constructor.
  • Updated Stream.fromIterable to send a done event after the error when the iterator's moveNext throws, and handle if the current getter throws (issue 33431).


  • Added HashMap.fromEntries and LinkedHashmap.fromEntries constructors.
  • Added ArgumentError.checkNotNull utility method.
  • Made Uri parsing more permissive about [ and ] occurring in the path, query or fragment, and # occurring in fragment.
  • Exported Future and Stream from dart:core.
  • Added operators &, | and ^ to bool.
  • Added missing methods to UnmodifiableMapMixin. Some maps intended to be unmodifiable incorrectly allowed new methods added in Dart 2 to succeed.
  • Deprecated the provisional annotation and the Provisional annotation class. These should have been removed before releasing Dart 2.0, and they have no effect.


Fixed Service Workers and any Promise/Future API with a Dictionary parameter.

APIs in dart:html (that take a Dictionary) will receive a Dart Map parameter. The Map parameter must be converted to a Dictionary before passing to the browser‘s API. Before this change, any Promise/Future API with a Map/Dictionary parameter never called the Promise and didn’t return a Dart Future - now it does.

This caused a number of breaks especially in Service Workers (register, etc.). Here is a complete list of the fixed APIs:

  • BackgroundFetchManager

    • Future<BackgroundFetchRegistration> fetch(String id, Object requests, [Map options])
  • CacheStorage

    • Future match(/*RequestInfo*/ request, [Map options])
  • CanMakePayment

    • Future<List<Client>> matchAll([Map options])
  • CookieStore

    • Future getAll([Map options])
    • Future set(String name, String value, [Map options])
  • CredentialsContainer

    • Future get([Map options])
    • Future create([Map options])
  • ImageCapture

    • Future setOptions(Map photoSettings)
  • MediaCapabilities

    • Future<MediaCapabilitiesInfo> decodingInfo(Map configuration)
    • Future<MediaCapabilitiesInfo> encodingInfo(Map configuration)
  • MediaStreamTrack

    • Future applyConstraints([Map constraints])
  • Navigator

    • Future requestKeyboardLock([List<String> keyCodes])
    • Future requestMidiAccess([Map options])
    • Future share([Map data])
  • OffscreenCanvas

    • Future<Blob> convertToBlob([Map options])
  • PaymentInstruments

    • Future set(String instrumentKey, Map details)
  • Permissions

    • Future<PermissionStatus> query(Map permission)
    • Future<PermissionStatus> request(Map permissions)
    • Future<PermissionStatus> revoke(Map permission)
  • PushManager

    • Future permissionState([Map options])
    • Future<PushSubscription> subscribe([Map options])
  • RtcPeerConnection

    • Changed:

      Future createAnswer([options_OR_successCallback,
          RtcPeerConnectionErrorCallback failureCallback,
          Map mediaConstraints])


      Future<RtcSessionDescription> createAnswer([Map options])
    • Changed:

      Future createOffer([options_OR_successCallback,
          RtcPeerConnectionErrorCallback failureCallback,
          Map rtcOfferOptions])


      Future<RtcSessionDescription> createOffer([Map options])
    • Changed:

      Future setLocalDescription(Map description,
          VoidCallback successCallback,
          [RtcPeerConnectionErrorCallback failureCallback])


      Future setLocalDescription(Map description)
    • Changed:

      Future setLocalDescription(Map description,
          VoidCallback successCallback,
          [RtcPeerConnectionErrorCallback failureCallback])


      Future setRemoteDescription(Map description)
  • ServiceWorkerContainer

    • Future<ServiceWorkerRegistration> register(String url, [Map options])
  • ServiceWorkerRegistration

    • Future<List<Notification>> getNotifications([Map filter])
    • Future showNotification(String title, [Map options])
  • VRDevice

    • Future requestSession([Map options])
    • Future supportsSession([Map options])
  • VRSession

    • Future requestFrameOfReference(String type, [Map options])
  • Window

    • Future fetch(/*RequestInfo*/ input, [Map init])
  • WorkerGlobalScope

    • Future fetch(/*RequestInfo*/ input, [Map init])

In addition, exposed Service Worker “self” as a static getter named “instance”. The instance is exposed on four different Service Worker classes and can throw a InstanceTypeError if the instance isn't of the class expected (WorkerGlobalScope.instance will always work and not throw):

  • SharedWorkerGlobalScope.instance
  • DedicatedWorkerGlobalScope.instance
  • ServiceWorkerGlobalScope.instance
  • WorkerGlobalScope.instance


  • Added new HTTP status codes.

Dart for the Web


  • (Breaking) Duplicate keys in a const map are not allowed and produce a compile-time error. Dart2js used to report this as a warning before. This was already an error in dartanalyzer and DDC and will be an error in other tools in the future as well.

  • Added -O flag to tune optimization levels. For more details run dart2js -h -v.

    We recommend to enable optimizations using the -O flag instead of individual flags for each optimization. This is because the -O flag is intended to be stable and continue to work in future versions of dart2js, while individual flags may come and go.

    At this time we recommend to test and debug with -O1 and to deploy with -O3.

Tool Changes


  • Addressed several dartfmt issues when used with the new CFE parser.


Bumped the linter to 0.1.70 which includes the following new lints:

  • avoid_returning_null_for_void
  • sort_pub_dependencies
  • prefer_mixin
  • avoid_implementing_value_types
  • flutter_style_todos
  • avoid_void_async
  • prefer_void_to_null

and improvements:

  • Fixed NPE in prefer_iterable_whereType.
  • Improved message display for await_only_futures
  • Performance improvements for null_closures
  • Mixin support
  • Updated sort_constructors_first to apply to all members.
  • Updated unnecessary_this to work on field initializers.
  • Updated unawaited_futures to ignore assignments within cascades.
  • Improved handling of constant expressions with generic type params.
  • NPE fix for invariant_booleans.
  • Improved docs for unawaited_futures.
  • Updated unawaited_futures to check cascades.
  • Relaxed void_checks (allowing T Function() to be assigned to void Function()).
  • Fixed false positives in lines_longer_than_80_chars.


  • Renamed the --checked flag to pub run to --enable-asserts.
  • Pub will no longer delete directories named “packages”.
  • The --packages-dir flag is now ignored.

2.0.0 - 2018-08-07

This is the first major version release of Dart since 1.0.0, so it contains many significant changes across all areas of the platform. Large changes include:

  • (Breaking) The unsound optional static type system has been replaced with a sound static type system using type inference and runtime checks. This was formerly called “strong mode” and only used by the Dart for web products. Now it is the one official static type system for the entire platform and replaces the previous “checked” and “production” modes.

  • (Breaking) Functions marked async now run synchronously until the first await statement. Previously, they would return to the event loop once at the top of the function body before any code runs (issue 30345).

  • (Breaking) Constants in the core libraries have been renamed from SCREAMING_CAPS to lowerCamelCase.

  • (Breaking) Many new methods have been added to core library classes. If you implement the interfaces of these classes, you will need to implement the new methods.

  • (Breaking) “dart:isolate” and “dart:mirrors” are no longer supported when using Dart for the web. They are still supported in the command-line VM.

  • (Breaking) Pub's transformer-based build system has been replaced by a new build system.

  • The new keyword is optional and can be omitted. Likewise, const can be omitted inside a const context (issue 30921).

  • Dartium is no longer maintained or supported.


  • Strong mode” is now the official type system of the language.

  • The new keyword is optional and can be omitted. Likewise, const can be omitted inside a const context.

  • A string in a part of declaration may now be used to refer to the library this file is part of. A library part can now declare its library as either:

    part of name.of.library;


    part of "uriReferenceOfLibrary.dart";

    This allows libraries with no library declarations (and therefore no name) to have parts, and it allows tools to easily find the library of a part file. The Dart 1.0 syntax is supported but deprecated.

  • Functions marked async now run synchronously until the first await statement. Previously, they would return to the event loop once at the top of the function body before any code runs (issue 30345).

  • The type void is now a Top type like dynamic, and Object. It also now has new errors for being used where not allowed (such as being assigned to any non-void-typed parameter). Some libraries (importantly, mockito) may need to be updated to accept void values to keep their APIs working.

  • Future flattening is now done only as specified in the Dart 2.0 spec, rather than more broadly. This means that the following code has an error on the assignment to y.

    test() {
      Future<int> f;
      var x = f.then<Future<List<int>>>((x) => []);
      Future<List<int>> y = x;
  • Invocations of noSuchMethod() receive default values for optional args. The following program used to print “No arguments passed”, and now prints “First argument is 3”.

    abstract class B {
      void m([int x = 3]);
    class A implements B {
      noSuchMethod(Invocation i) {
        if (i.positionalArguments.length == 0) {
          print("No arguments passed");
        } else {
          print("First argument is ${i.positionalArguments[0]}");
    void main() {
  • Bounds on generic functions are invariant. The following program now issues an invalid override error (issue 29014):

    class A {
      void f<T extends int>() {}
    class B extends A {
      void f<T extends num>() {}
  • Numerous corner case bugs around return statements in synchronous and asynchronous functions fixed. Specifically:

    • Issues 31887, 32881. Future flattening should not be recursive.
    • Issues 30638, 32233. Incorrect downcast errors with FutureOr.
    • Issue 32233. Errors when returning FutureOr.
    • Issue 33218. Returns in functions with void related types.
    • Issue 31278. Incorrect hint on empty returns in async. functions.
  • An empty return; in an async function with return type Future<Object> does not report an error.

  • return exp; where exp has type void in an async function is now an error unless the return type of the function is void or dynamic.

  • Mixed return statements of the form return; and return exp; are now allowed when exp has type void.

  • A compile time error is emitted for any literal which cannot be exactly represented on the target platform. As a result, dart2js and DDC report errors if an integer literal cannot be represented exactly in JavaScript (issue 33282).

  • New member conflict rules have been implemented. Most cases of conflicting members with the same name are now static errors (issue 33235).

Core libraries

  • Replaced UPPER_CASE constant names with lowerCamelCase. For example, HTML_ESCAPE is now htmlEscape.

  • The Web libraries were re-generated using Chrome 63 WebIDLs (details).


  • Stream:
    • Added cast and castFrom.
    • Changed firstWhere, lastWhere, and singleWhere to return Future<T> and added an optional T orElse() callback.
  • StreamTransformer: added cast and castFrom.
  • StreamTransformerBase: new class.
  • Timer: added tick property.
  • Zone
    • changed to be strong-mode clean. This required some breaking API changes. See https://goo.gl/y9mW2x for more information.
    • Added bindBinaryCallbackGuarded, bindCallbackGuarded, and bindUnaryCallbackGuarded.
    • Renamed Zone.ROOT to Zone.root.
  • Removed the deprecated defaultValue parameter on Stream.firstWhere and Stream.lastWhere.
  • Changed an internal lazily-allocated reusable “null future” to always belong to the root zone. This avoids race conditions where the first access to the future determined which zone it would belong to. The zone is only used for scheduling the callback of listeners, the listeners themselves will run in the correct zone in any case. Issue #32556.


  • New “provisional” library for CLI-specific features.
  • waitFor: function that suspends a stack to wait for a Future to complete.


  • MapBase: added mapToString.
  • LinkedHashMap no longer implements HashMap
  • LinkedHashSet no longer implements HashSet.
  • Added of constructor to Queue, ListQueue, DoubleLinkedQueue, HashSet, LinkedHashSet, SplayTreeSet, Map, HashMap, LinkedHashMap, SplayTreeMap.
  • Removed Maps class. Extend MapBase or mix in MapMixin instead to provide map method implementations for a class.
  • Removed experimental Document method getCSSCanvasContext and property supportsCssCanvasContext.
  • Removed obsolete Element property xtag no longer supported in browsers.
  • Exposed ServiceWorker class.
  • Added constructor to MessageChannel and MessagePort addEventListener automatically calls start method to receive queued messages.


  • Base64Codec.decode return type is now Uint8List.
  • JsonUnsupportedObjectError: added partialResult property
  • LineSplitter now implements StreamTransformer<String, String> instead of Converter. It retains Converter methods convert and startChunkedConversion.
  • Utf8Decoder when compiled with dart2js uses the browser's TextDecoder in some common cases for faster decoding.
  • Renamed ASCII, BASE64, BASE64URI, JSON, LATIN1 and UTF8 to ascii, base64, base64Uri, json, latin1 and utf8.
  • Renamed the HtmlEscapeMode constants UNKNOWN, ATTRIBUTE, SQ_ATTRIBUTE and ELEMENT to unknown, attribute, sqAttribute and elements.
  • Added jsonEncode, jsonDecode, base64Encode, base64UrlEncode and base64Decode top-level functions.
  • Changed return type of encode on AsciiCodec and Latin1Codec, and convert on AsciiEncoder, Latin1Encoder, to Uint8List.
  • Allow utf8.decoder.fuse(json.decoder) to ignore leading Unicode BOM.


  • BigInt class added to support integers greater than 64-bits.
  • Deprecated the proxy annotation.
  • Added Provisional class and provisional field.
  • Added pragma annotation.
  • RegExp added static escape function.
  • The Uri class now correctly handles paths while running on Node.js on Windows.
  • Core collection changes:
    • Iterable added members cast, castFrom, followedBy and whereType.
    • Iterable.singleWhere added orElse parameter.
    • List added + operator, first and last setters, and indexWhere and lastIndexWhere methods, and static copyRange and writeIterable methods.
    • Map added fromEntries constructor.
    • Map added addEntries, cast, entries, map, removeWhere, update and updateAll members.
    • MapEntry: new class used by Map.entries.
    • Note: if a class extends IterableBase, ListBase, SetBase or MapBase (or uses the corresponding mixins) from dart:collection, the new members are implemented automatically.
    • Added of constructor to List, Set, Map.
  • Renamed double.INFINITY, double.NEGATIVE_INFINITY, double.NAN, double.MAX_FINITE and double.MIN_POSITIVE to double.infinity, double.negativeInfinity, double.nan, double.maxFinite and double.minPositive.
  • Renamed the following constants in DateTime to lower case: MONDAY through SUNDAY, DAYS_PER_WEEK (as daysPerWeek), JANUARY through DECEMBER and MONTHS_PER_YEAR (as monthsPerYear).
  • Renamed the following constants in Duration to lower case: MICROSECONDS_PER_MILLISECOND to microsecondsPerMillisecond, MILLISECONDS_PER_SECOND to millisecondsPerSecond, SECONDS_PER_MINUTE to secondsPerMinute, MINUTES_PER_HOUR to minutesPerHour, HOURS_PER_DAY to hoursPerDay, MICROSECONDS_PER_SECOND to microsecondsPerSecond, MICROSECONDS_PER_MINUTE to microsecondsPerMinute, MICROSECONDS_PER_HOUR to microsecondsPerHour, MICROSECONDS_PER_DAY to microsecondsPerDay, MILLISECONDS_PER_MINUTE to millisecondsPerMinute, MILLISECONDS_PER_HOUR to millisecondsPerHour, MILLISECONDS_PER_DAY to millisecondsPerDay, SECONDS_PER_HOUR to secondsPerHour, SECONDS_PER_DAY to secondsPerDay, MINUTES_PER_DAY to minutesPerDay, and ZERO to zero.
  • Added typeArguments to Invocation class.
  • Added constructors to invocation class that allows creation of Invocation objects directly, without going through noSuchMethod.
  • Added unaryMinus and empty constant symbols on the Symbol class.
  • Changed return type of UriData.dataAsBytes to Uint8List.
  • Added tryParse static method to int, double, num, BigInt, Uri and DateTime.
  • Deprecated onError parameter on int.parse, double.parse and num.parse.
  • Deprecated the NoSuchMethodError constructor.
  • int.parse on the VM no longer accepts unsigned hexadecimal numbers greater than or equal to 2**63 when not prefixed by 0x. (SDK issue 32858)


  • Flow class added.
  • Timeline.startSync and Timeline.timeSync now accepts an optional parameter flow of type Flow. The flow parameter is used to generate flow timeline events that are enclosed by the slice described by Timeline.{start,finish}Sync and Timeline.timeSync.


  • Removed deprecated query and queryAll. Use querySelector and querySelectorAll.


  • HttpStatus added UPGRADE_REQUIRED.
  • IOOverrides and HttpOverrides added to aid in writing tests that wish to mock varios dart:io objects.
  • Platform.operatingSystemVersion added that gives a platform-specific String describing the version of the operating system.
  • ProcessStartMode.INHERIT_STDIO added, which allows a child process to inherit the parent's stdio handles.
  • RawZLibFilter added for low-level access to compression and decompression routines.
  • Unified backends for SecureSocket, SecurityContext, and X509Certificate to be consistent across all platforms. All SecureSocket, SecurityContext, and X509Certificate properties and methods are now supported on iOS and OSX.
  • SecurityContext.alpnSupported deprecated as ALPN is now supported on all platforms.
  • SecurityContext: added withTrustedRoots named optional parameter constructor, which defaults to false.
  • Added a timeout parameter to Socket.connect, RawSocket.connect, SecureSocket.connect and RawSecureSocket.connect. If a connection attempt takes longer than the duration specified in timeout, a SocketException will be thrown. Note: if the duration specified in timeout is greater than the OS level timeout, a timeout may occur sooner than specified in timeout.
  • Stdin.hasTerminal added, which is true if stdin is attached to a terminal.
  • WebSocket added static userAgent property.
  • RandomAccessFile.close returns Future<void>
  • Added IOOverrides.socketConnect.
  • Added Dart-styled constants to ZLibOptions, FileMode, FileLock, FileSystemEntityType, FileSystemEvent, ProcessStartMode, ProcessSignal, InternetAddressType, InternetAddress, SocketDirection, SocketOption, RawSocketEvent, and StdioType, and deprecated the old SCREAMING_CAPS constants.
  • Added the Dart-styled top-level constants zlib, gzip, and systemEncoding, and deprecated the old SCREAMING_CAPS top-level constants.
  • Removed the top-level FileMode constants READ, WRITE, APPEND, WRITE_ONLY, and WRITE_ONLY_APPEND. Please use e.g. FileMode.read instead.
  • Added X509Certificate.der, X509Certificate.pem, and X509Certificate.sha1.
  • Added FileSystemEntity.fromRawPath constructor to allow for the creation of FileSystemEntity using Uint8List buffers.
  • Dart-styled constants have been added for HttpStatus, HttpHeaders, ContentType, HttpClient, WebSocketStatus, CompressionOptions, and WebSocket. The SCREAMING_CAPS constants are marked deprecated. Note that HttpStatus.CONTINUE is now HttpStatus.continue_, and that e.g. HttpHeaders.FIELD_NAME is now HttpHeaders.fieldNameHeader.
  • Deprecated Platform.packageRoot, which is only used for packages/ directory resolution which is no longer supported. It will now always return null, which is a value that was always possible for it to return previously.
  • Adds HttpClient.connectionTimeout.
  • Adds {Socket,RawSocket,SecureSocket}.startConnect. These return a ConnectionTask, which can be used to cancel an in-flight connection attempt.


  • Make Isolate.spawn take a type parameter representing the argument type of the provided function. This allows functions with arguments types other than Object in strong mode.
  • Rename IMMEDIATE and BEFORE_NEXT_EVENT on Isolate to immediate and beforeNextEvent.
  • Deprecated Isolate.packageRoot, which is only used for packages/ directory resolution which is no longer supported. It will now always return null, which is a value that was always possible for it to return previously.
  • Deprecated packageRoot parameter in Isolate.spawnUri, which is was previously used only for packages/ directory resolution. That style of resolution is no longer supported in Dart 2.


  • Renamed E, LN10, LN, LOG2E, LOG10E, PI, SQRT1_2 and SQRT2 to e, ln10, ln, log2e, log10e, pi, sqrt1_2 and sqrt2.


  • Added IsolateMirror.loadUri, which allows dynamically loading additional code.
  • Marked MirrorsUsed as deprecated. The MirrorsUsed annotation was only used to inform the dart2js compiler about how mirrors were used, but dart2js no longer supports the mirrors library altogether.


  • Added Unmodifiable view classes over all List types.
  • Renamed BYTES_PER_ELEMENT to bytesPerElement on all typed data lists.
  • Renamed constants XXXX through WWWW on Float32x4 and Int32x4 to lower-case xxxx through wwww.
  • Renamed Endinanness to Endian and its constants from BIG_ENDIAN, LITTLE_ENDIAN and HOST_ENDIAN to little, big and host.

Dart VM

  • Support for MIPS has been removed.

  • Dart int is now restricted to 64 bits. On overflow, arithmetic operations wrap around, and integer literals larger than 64 bits are not allowed. See https://github.com/dart-lang/sdk/blob/master/docs/language/informal/int64.md for details.

  • The Dart VM no longer attempts to perform packages/ directory resolution (for loading scripts, and in Isolate.resolveUri). Users relying on packages/ directories should switch to .packages files.

Dart for the Web

  • Expose JavaScript Promise APIs using Dart futures. For example, BackgroundFetchManager.get is defined as:

      Future<BackgroundFetchRegistration> get(String id)

    It can be used like:

    BackgroundFetchRegistration result = await fetchMgr.get('abc');

    The underlying JS Promise-to-Future mechanism will be exposed as a public API in the future.

Dart Dev Compiler (DDC)

  • dartdevc will no longer throw an error from is checks that return a different result in weak mode (SDK issue 28988). For example:

    main() {
      List l = [];
      // Prints "false", does not throw.
      print(l is List<String>);
  • Failed as casts on Iterable<T>, Map<T>, Future<T>, and Stream<T> are no longer ignored. These failures were ignored to make it easier to migrate Dart 1 code to strong mode, but ignoring them is a hole in the type system. This closes part of that hole. (We still need to stop ignoring “as” cast failures on function types, and implicit cast failures on the above types and function types.)


  • dart2js now compiles programs with Dart 2.0 semantics. Apps are expected to be bigger than before, because Dart 2.0 has many more implicit checks (similar to the --checked flag in Dart 1.0).

    We exposed a --omit-implicit-checks flag which removes most of the extra implicit checks. Only use this if you have enough test coverage to know that the app will work well without the checks. If a check would have failed and it is omitted, your app may crash or behave in unexpected ways. This flag is similar to --trust-type-annotations in Dart 1.0.

  • dart2js replaced its front-end with the common front-end (CFE). Thanks to the CFE, dart2js errors are more consistent with all other Dart tools.

  • dart2js replaced its source-map implementation. There aren't any big differences, but more data is emitted for synthetic code generated by the compiler.

  • dart:mirrors support was removed. Frameworks are encouraged to use code-generation instead. Conditional imports indicate that mirrors are not supported, and any API in the mirrors library will throw at runtime.

  • The generated output of dart2js can now be run as a webworker.

  • dart:isolate support was removed. To launch background tasks, please use webworkers instead. APIs for webworkers can be accessed from dart:html or JS-interop.

  • dart2js no longer supports the --package-root flag. This flag was deprecated in favor of --packages long ago.

Tool Changes


  • The analyzer will no longer issue a warning when a generic type parameter is used as the type in an instance check. For example:

    test<T>() {
      print(3 is T); // No warning
  • New static checking of @visibleForTesting elements. Accessing a method, function, class, etc. annotated with @visibleForTesting from a file not in a test/ directory will result in a new hint (issue 28273).

  • Static analysis now respects functions annotated with @alwaysThrows (issue 31384).

  • New hints added:

    • NULL_AWARE_BEFORE_OPERATOR when an operator is used after a null-aware access. For example:

      x?.a - ''; // HINT
    • NULL_AWARE_IN_LOGICAL_OPERATOR when an expression with null-aware access is used as a condition in logical operators. For example:

      x.a || x?.b; // HINT
  • The command line analyzer (dartanalyzer) and the analysis server no longer treat directories named packages specially. Previously they had ignored these directories - and their contents - from the point of view of analysis. Now they'll be treated just as regular directories. This special-casing of packages directories was to support using symlinks for package: resolution; that functionality is now handled by .packages files.

  • New static checking of duplicate shown or hidden names in an export directive (issue 33182).

  • The analysis server will now only analyze code in Dart 2 mode (‘strong mode’). It will emit warnings for analysis options files that have strong-mode: false set (and will emit a hint for strong-mode: true, which is no longer necessary).

  • The dartanalyzer --strong flag is now deprecated and ignored. The command-line analyzer now only analyzes code in strong mode.


  • Support assert() in const constructor initializer lists.

  • Better formatting for multi-line strings in argument lists.

  • Force splitting an empty block as the then body of an if with an else.

  • Support metadata annotations on enum cases.

  • Add --fix to remove unneeded new and const keywords, and change : to = before named parameter default values.

  • Change formatting rules around static methods to uniformly format code with and without new and const.

  • Format expressions inside string interpolation.


  • Pub has a brand new version solver! It supports all the same features as the old version solver, but it‘s much less likely to stall out on difficult package graphs, and it’s much clearer about why a solution can't be found when version solving fails.

  • Remove support for transformers, pub build, and pub serve. Use the new build system instead.

  • There is now a default SDK constraint of <2.0.0 for any package with no existing upper bound. This allows us to move more safely to 2.0.0. All new packages published on pub will now require an upper bound SDK constraint so future major releases of Dart don't destabilize the package ecosystem.

    All SDK constraint exclusive upper bounds are now treated as though they allow pre-release versions of that upper bound. For example, the SDK constraint >=1.8.0 <2.0.0 now allows pre-release SDK versions such as 2.0.0-beta.3.0. This allows early adopters to try out packages that don't explicitly declare support for the new version yet. You can disable this functionality by setting the PUB_ALLOW_PRERELEASE_SDK environment variable to false.

  • Allow depending on a package in a subdirectory of a Git repository. Git dependencies may now include a path parameter, indicating that the package exists in a subdirectory of the Git repository. For example:

          url: git://github.com/dart-lang/multi_package_repo
          path: pkg/foobar
  • Added an --executables option to pub deps command. This will list all available executables that can be run with pub run.

  • The Flutter sdk source will now look for packages in flutter/bin/cache/pkg/ as well as flutter/packages/. In particular, this means that packages can depend on the sky_engine package from the sdk source (issue 1775).

  • Pub now caches compiled packages and snapshots in the .dart_tool/pub directory, rather than the .pub directory (issue 1795).

  • Other bug fixes and improvements.

1.24.3 - 2017-12-14

  • Fix for constructing a new SecurityContext that contains the built-in certificate authority roots (issue 24693).

Core library changes

  • dart:io
    • Unified backends for SecureSocket, SecurityContext, and X509Certificate to be consistent across all platforms. All SecureSocket, SecurityContext, and X509Certificate properties and methods are now supported on iOS and OSX.

1.24.2 - 2017-06-22

  • Fixes for debugging in Dartium.
    • Fix DevConsole crash with JS (issue 29873).
    • Fix debugging in WebStorm, NULL returned for JS objects (issue 29854).

1.24.1 - 2017-06-14

  • Bug fixes for dartdevc support in pub serve.
    • Fixed module config invalidation logic so modules are properly recalculated when package layout changes.
    • Fixed exception when handling require.js errors that aren't script load errors.
    • Fixed an issue where requesting the bootstrap.js file before the dart.js file would result in a 404.
    • Fixed a Safari issue during bootstrapping (note that Safari is still not officially supported but does work for trivial examples).
  • Fix for a Dartium issue where there was no sound in checked mode (issue 29810).

1.24.0 - 2017-06-12


  • During a dynamic type check, void is not required to be null anymore. In practice, this makes overriding void functions with non-void functions safer.

  • During static analysis, a function or setter declared using => with return type void now allows the returned expression to have any type. For example, assuming the declaration int x;, it is now type correct to have void f() => ++x;.

  • A new function-type syntax has been added to the language. Warning: In Dart 1.24, this feature is incomplete, and not stable in the Analyzer.

    Intuitively, the type of a function can be constructed by textually replacing the function's name with Function in its declaration. For instance, the type of void foo() {} would be void Function(). The new syntax may be used wherever a type can be written. It is thus now possible to declare fields containing functions without needing to write typedefs: void Function() x;. The new function type has one restriction: it may not contain the old-style function-type syntax for its parameters. The following is thus illegal: void Function(int f()). typedefs have been updated to support this new syntax.


    typedef F = void Function();  // F is the name for a `void` callback.
    int Function(int) f;  // A field `f` that contains an int->int function.
    class A<T> {
      // The parameter `callback` is a function that takes a `T` and returns
      // `void`.
      void forEach(void Function(T) callback);
    // The new function type supports generic arguments.
    typedef Invoker = T Function<T>(T Function() callback);

Core library changes

  • dart:async, dart:core, dart:io

    • Adding to a closed sink, including IOSink, is no longer not allowed. In 1.24, violations are only reported (on stdout or stderr), but a future version of the Dart SDK will change this to throwing a StateError.
  • dart:convert

    • BREAKING Removed the deprecated ChunkedConverter class.
    • JSON maps are now typed as Map<String, dynamic> instead of Map<dynamic, dynamic>. A JSON-map is not a HashMap or LinkedHashMap anymore (but just a Map).
  • dart:io

    • Added Platform.localeName, needed for accessing the locale on platforms that don't store it in an environment variable.
    • Added ProcessInfo.currentRss and ProcessInfo.maxRss for inspecting the Dart VM process current and peak resident set size.
    • Added RawSynchronousSocket, a basic synchronous socket implementation.
  • dart: web APIs have been updated to align with Chrome v50. This change includes a large number of changes, many of which are breaking. In some cases, new class names may conflict with names that exist in existing code.

  • dart:html

    • REMOVED classes: Bluetooth, BluetoothDevice, BluetoothGattCharacteristic, BluetoothGattRemoteServer, BluetoothGattService, BluetoothUuid, CrossOriginConnectEvent, DefaultSessionStartEvent, DomSettableTokenList, MediaKeyError, PeriodicSyncEvent, PluginPlaceholderElement, ReadableStream, StashedMessagePort, SyncRegistration

    • REMOVED members:

      • texImage2DCanvas was removed from RenderingContext.
      • endClip and startClip were removed from Animation.
      • after and before were removed from CharacterData, ChildNode and Element.
      • keyLocation was removed from KeyboardEvent. Use location instead.
      • generateKeyRequest, keyAddedEvent, keyErrorEvent, keyMessageEvent, mediaGroup, needKeyEvent, onKeyAdded, onKeyError, onKeyMessage, and onNeedKey were removed from MediaElement.
      • getStorageUpdates was removed from Navigator
      • status was removed from PermissionStatus
      • getAvailability was removed from PreElement
    • Other behavior changes:

      • URLs returned in CSS or html are formatted with quoted string. Like url("http://google.com") instead of url(http://google.com).
      • Event timestamp property type changed from int to num.
      • Chrome introduced slight layout changes of UI objects. In addition many height/width dimensions are returned in subpixel values (num instead of whole numbers).
      • setRangeText with a selectionMode value of ‘invalid’ is no longer valid. Only “select”, “start”, “end”, “preserve” are allowed.
  • dart:svg

    • A large number of additions and removals. Review your use of dart:svg carefully.
  • dart:web_audio

    • new method on AudioContext - createIirFilter returns a new class IirFilterNode.
  • dart:web_gl

    • new classes: CompressedTextureAstc, ExtColorBufferFloat, ExtDisjointTimerQuery, and TimerQueryExt.

    • ExtFragDepth added: readPixels2 and texImage2D2.

Strong Mode

  • Removed ad hoc Future.then inference in favor of using FutureOr. Prior to adding FutureOr to the language, the analyzer implemented an ad hoc type inference for Future.then (and overrides) treating it as if the onValue callback was typed to return FutureOr for the purposes of inference. This ad hoc inference has been removed now that FutureOr has been added.

    Packages that implement Future must either type the onValue parameter to .then as returning FutureOr<T>, or else must leave the type of the parameter entirely to allow inference to fill in the type.

  • During static analysis, a function or setter declared using => with return type void now allows the returned expression to have any type.

Tool Changes

  • Dartium

    Dartium is now based on Chrome v50. See Core library changes above for details on the changed APIs.

  • Pub

    • pub build and pub serve

      • Added support for the Dart Development Compiler.

        Unlike dart2js, this new compiler is modular, which allows pub to do incremental re-builds for pub serve, and potentially pub build in the future.

        In practice what that means is you can edit your Dart files, refresh in Chrome (or other supported browsers), and see your edits almost immediately. This is because pub is only recompiling your package, not all packages that you depend on.

        There is one caveat with the new compiler, which is that your package and your dependencies must all be strong mode clean. If you are getting an error compiling one of your dependencies, you will need to file bugs or send pull requests to get them strong mode clean.

        There are two ways of opting into the new compiler:

        • Use the new --web-compiler flag, which supports dartdevc, dart2js or none as options. This is the easiest way to try things out without changing the default.

        • Add config to your pubspec. There is a new web key which supports a single key called compiler. This is a map from mode names to compiler to use. For example, to default to dartdevc in debug mode you can add the following to your pubspec:

              debug: dartdevc

        You can also use the new compiler to run your tests in Chrome much more quickly than you can with dart2js. In order to do that, run pub serve test --web-compiler=dartdevc, and then run pub run test -p chrome --pub-serve=8080.

      • The --no-dart2js flag has been deprecated in favor of --web-compiler=none.

      • pub build will use a failing exit code if there are errors in any transformer.

    • pub publish

      • Added support for the UNLICENSE file.

      • Packages that depend on the Flutter SDK may be published.

    • pub get and pub upgrade

      • Don't dump a stack trace when a network error occurs while fetching packages.
  • dartfmt

    • Preserve type parameters in new generic function typedef syntax.
    • Add self-test validation to ensure formatter bugs do not cause user code to be lost.

Infrastructure changes

  • As of this release, we‘ll show a warning when using the MIPS architecture. Unless we learn about any critical use of Dart on MIPS in the meantime, we’re planning to deprecate support for MIPS starting with the next stable release.

1.23.0 - 2017-04-21

Strong Mode

  • Breaking change - it is now a strong mode error if a mixin causes a name conflict between two private members (field/getter/setter/method) from a different library. (SDK issue 28809).


class A {
  int _x;

class B {
  int _x;


import 'lib1.dart';

class C extends A with B {}
    error • The private name _x, defined by B, conflicts with the same name defined by A at tmp/lib2.dart:3:24 • private_collision_in_mixin_application
  • Breaking change - strong mode will prefer the expected type to infer generic types, functions, and methods (SDK issue 27586).

    main() {
      List<Object> foo = /*infers: <Object>*/['hello', 'world'];
      var bar = /*infers: <String>*/['hello', 'world'];
  • Strong mode inference error messages are improved (SDK issue 29108).

    import 'dart:math';
    test(Iterable/* fix is to add <num> here */ values) {
      num n = values.fold(values.first as num, max);

    Now produces the error on the generic function “max”:

    Couldn't infer type parameter 'T'.
    Tried to infer 'dynamic' for 'T' which doesn't work:
      Function type declared as '<T extends num>(T, T) → T'
                    used where  '(num, dynamic) → num' is required.
    Consider passing explicit type argument(s) to the generic.
  • Strong mode supports overriding fields, @virtual is no longer required (SDK issue 28120).

    class C {
      int x = 42;
    class D extends C {
      get x {
        print("x got called");
        return super.x;
    main() {
      print(new D().x);
  • Strong mode down cast composite warnings are no longer issued by default. (SDK issue 28588).

void test() {
  List untyped = [];
  List<int> typed = untyped; // No down cast composite warning

To opt back into the warnings, add the following to the .analysis_options file for your project.

    strong_mode_down_cast_composite: warning

Core library changes

  • dart:core
    • Added Uri.isScheme function to check the scheme of a URI. Example: uri.isScheme("http"). Ignores case when comparing.
    • Make UriData.parse validate its input better. If the data is base-64 encoded, the data is normalized wrt. alphabet and padding, and it contains invalid base-64 data, parsing fails. Also normalizes non-base-64 data.
  • dart:io
    • Added functions File.lastAccessed, File.lastAccessedSync, File.setLastModified, File.setLastModifiedSync, File.setLastAccessed, and File.setLastAccessedSync.
    • Added {Stdin,Stdout}.supportsAnsiEscapes.

Dart VM

  • Calls to print() and Stdout.write*() now correctly print unicode characters to the console on Windows. Calls to Stdout.add*() behave as before.

Tool changes

  • Analysis

    • dartanalyzer now follows the same rules as the analysis server to find an analysis options file, stopping when an analysis options file is found:
      • Search up the directory hierarchy looking for an analysis options file.
      • If analyzing a project referencing the Flutter package, then use the default Flutter analysis options found in package:flutter.
      • If in a Bazel workspace, then use the analysis options in package:dart.analysis_options/default.yaml if it exists.
      • Use the default analysis options rules.
    • In addition, specific to dartanalyzer:
      • an analysis options file can be specified on the command line via --options and that file will be used instead of searching for an analysis options file.
      • any analysis option specified on the command line (e.g. --strong or --no-strong) takes precedence over any corresponding value specified in the analysis options file.
  • Dartium, dart2js, and DDC

    • Imports to dart:io are allowed, but the imported library is not supported and will likely fail on most APIs at runtime. This change was made as a stopgap measure to make it easier to write libraries that share code between platforms (like package http). This might change again when configuration specific imports are supported.
  • Pub

    • Now sends telemetry data to pub.dartlang.org to allow better understanding of why a particular package is being accessed.
    • pub publish
      • Warns if a package imports a package that‘s not a dependency from within lib/ or bin/, or a package that’s not a dev dependency from within benchmark/, example/, test/ or tool/.
      • No longer produces “UID too large” errors on OS X. All packages are now uploaded with the user and group names set to “pub”.
      • No longer fails with a stack overflow when uploading a package that uses Git submodules.
    • pub get and pub upgrade
      • Produce more informative error messages if they're run directly in a package that uses Flutter.
      • Properly unlock SDK and path dependencies if they have a new version that‘s also valid according to the user’s pubspec.
  • dartfmt

    • Support new generic function typedef syntax.
    • Make the precedence of cascades more visible.
    • Fix a couple of places where spurious newlines were inserted.
    • Correctly report unchanged formatting when reading from stdin.
    • Ensure space between - and --. Code that does this is pathological, but it technically meant dartfmt could change the semantics of the code.
    • Preserve a blank line between enum cases.
    • Other small formatting tweaks.

1.22.1 - 2017-02-22

Patch release, resolves two issues:

1.22.0 - 2017-02-14


  • Breaking change: ‘Generalized tear-offs’ are no longer supported, and will cause errors. We updated the language spec and added warnings in 1.21, and are now taking the last step to fully de-support them. They were previously only supported in the VM, and there are almost no known uses of them in the wild.

  • The assert() statement has been expanded to support an optional second message argument (SDK issue 27342).

    The message is displayed if the assert fails. It can be any object, and it is accessible as AssertionError.message. It can be used to provide more user friendly exception outputs. As an example, the following assert:

    assert(configFile != null, "Tool config missing. Please see https://goo.gl/k8iAi for details.");

    would produce the following exception output:

    Unhandled exception:
    'file:///Users/mit/tmp/tool/bin/main.dart': Failed assertion: line 9 pos 10:
    'configFile != null': Tool config missing. Please see https://goo.gl/k8iAi for details.
    #0      _AssertionError._doThrowNew (dart:core-patch/errors_patch.dart:33)
    #1      _AssertionError._throwNew (dart:core-patch/errors_patch.dart:29)
    #2      main (file:///Users/mit/tmp/tool/bin/main.dart:9:10)
  • The Null type has been moved to the bottom of the type hierarchy. As such, it is considered a subtype of every other type. The null literal was always treated as a bottom type. Now the named class Null is too:

    const empty = <Null>[];
    String concatenate(List<String> parts) => parts.join();
    int sum(List<int> numbers) => numbers.fold(0, (sum, n) => sum + n);
    concatenate(empty); // OK.
    sum(empty); // OK.
  • Introduce covariant modifier on parameters. It indicates that the parameter (and the corresponding parameter in any method that overrides it) has looser override rules. In strong mode, these require a runtime type check to maintain soundness, but enable an architectural pattern that is useful in some code.

    It lets you specialize a family of classes together, like so:

    abstract class Predator {
      void chaseAndEat(covariant Prey p);
    abstract class Prey {}
    class Mouse extends Prey {}
    class Seal extends Prey {}
    class Cat extends Predator {
      void chaseAndEat(Mouse m) => ...
    class Orca extends Predator {
      void chaseAndEat(Seal s) => ...

    This isn't statically safe, because you could do:

    Predator predator = new Cat(); // Upcast.
    predator.chaseAndEat(new Seal()); // Cats can't eat seals!

    To preserve soundness in strong mode, in the body of a method that uses a covariant override (here, Cat.chaseAndEat()), the compiler automatically inserts a check that the parameter is of the expected type. So the compiler gives you something like:

    class Cat extends Predator {
      void chaseAndEat(o) {
        var m = o as Mouse;

    Spec mode allows this unsound behavior on all parameters, even though users rarely rely on it. Strong mode disallowed it initially. Now, strong mode lets you opt into this behavior in the places where you do want it by using this modifier. Outside of strong mode, the modifier is ignored.

  • Change instantiate-to-bounds rules for generic type parameters when running in strong mode. If you leave off the type parameters from a generic type, we need to decide what to fill them in with. Dart 1.0 says just use dynamic, but that isn't sound:

    class Abser<T extends num> {
       void absThis(T n) { n.abs(); }
    var a = new Abser(); // Abser<dynamic>.
    a.absThis("not a num");

    We want the body of absThis() to be able to safely assume n is at least a num -- that‘s why there’s a constraint on T, after all. Implicitly using dynamic as the type parameter in this example breaks that.

    Instead, strong mode uses the bound. In the above example, it fills it in with num, and then the second line where a string is passed becomes a static error.

    However, there are some cases where it is hard to figure out what that default bound should be:

    class RuhRoh<T extends Comparable<T>> {}

    Strong mode‘s initial behavior sometimes produced surprising, unintended results. For 1.22, we take a simpler approach and then report an error if a good default type argument can’t be found.

Core libraries

  • Define FutureOr<T> for code that works with either a future or an immediate value of some type. For example, say you do a lot of text manipulation, and you want a handy function to chain a bunch of them:

    typedef String StringSwizzler(String input);
    String swizzle(String input, List<StringSwizzler> swizzlers) {
      var result = input;
      for (var swizzler in swizzlers) {
        result = swizzler(result);
      return result;

    This works fine:

    main() {
      var result = swizzle("input", [
        (s) => s.toUpperCase(),
        (s) => () => s * 2)
      print(result); // "INPUTINPUT".

    Later, you realize you'd also like to support swizzlers that are asynchronous (maybe they look up synonyms for words online). You could make your API strictly asynchronous, but then users of simple synchronous swizzlers have to manually wrap the return value in a Future.value(). Ideally, your swizzle() function would be “polymorphic over asynchrony”. It would allow both synchronous and asynchronous swizzlers. Because await accepts immediate values, it is easy to implement this dynamically:

    Future<String> swizzle(String input, List<StringSwizzler> swizzlers) async {
      var result = input;
      for (var swizzler in swizzlers) {
        result = await swizzler(result);
      return result;
    main() async {
      var result = swizzle("input", [
        (s) => s.toUpperCase(),
        (s) => new Future.delayed(new Duration(milliseconds: 40), () => s * 2)
      print(await result);

    What should the declared return type on StringSwizzler be? In the past, you had to use dynamic or Object, but that doesn't tell the user much. Now, you can do:

    typedef FutureOr<String> StringSwizzler(String input);

    Like the name implies, FutureOr<String> is a union type. It can be a String or a Future<String>, but not anything else. In this case, that's not super useful beyond just stating a more precise type for readers of the code. It does give you a little better error checking in code that uses the result of that.

    FutureOr<T> becomes really important in generic methods like Future.then(). In those cases, having the type system understand this magical union type helps type inference figure out the type argument of then() based on the closure you pass it.

    Previously, strong mode had hard-coded rules for handling Future.then() specifically. FutureOr<T> exposes that functionality so third-party APIs can take advantage of it too.

Tool changes

  • Dart2Js

    • Remove support for (long-time deprecated) mixin typedefs.
  • Pub

    • Avoid using a barback asset server for executables unless they actually use transformers. This makes precompilation substantially faster, produces better error messages when precompilation fails, and allows globally-activated executables to consistently use the Isolate.resolvePackageUri() API.

    • On Linux systems, always ignore packages' original file owners and permissions when extracting those packages. This was already the default under most circumstances.

    • Properly close the standard input stream of child processes started using pub run.

    • Handle parse errors from the package cache more gracefully. A package whose pubspec can't be parsed will now be ignored by pub get --offline and deleted by pub cache repair.

    • Make pub run run executables in spawned isolates. This lets them handle signals and use standard IO reliably.

    • Fix source-maps produced by dart2js when running in pub serve: URL references to assets from packages match the location where pub serve serves them (packages/package_name/ instead of ../packages/package_name/).

Infrastructure changes

  • The SDK now uses GN rather than gyp to generate its build files, which will now be exclusively ninja flavored. Documentation can be found on our wiki. Also see the help message of tools/gn.py. This change is in response to the deprecation of gyp. Build file generation with gyp will continue to be available in this release by setting the environment variable DART_USE_GYP before running gclient sync or gclient runhooks, but this will be removed in a future release.

1.21.1 - 2017-01-13

Patch release, resolves one issue:

  • Dart VM: Snapshots of generic functions fail. Issue 28072

1.21.0 - 2016-12-07


  • Support generic method syntax. Type arguments are not available at runtime. For details, check the informal specification.

  • Support access to initializing formals, e.g., the use of x to initialize y in class C { var x, y; C(this.x): y = x; }. Please check the informal specification for details.

  • Don't warn about switch case fallthrough if the case ends in a rethrow statement. (SDK issue 27650)

  • Also don't warn if the entire switch case is wrapped in braces - as long as the block ends with a break, continue, rethrow, return or throw.

  • Allow = as well as : as separator for named parameter default values.

    enableFlags({bool hidden: false}) {}

    can now be replaced by

    enableFlags({bool hidden = false}) {}

    (SDK issue 27559)

Core library changes

  • dart:core: Set.difference now takes a Set<Object> as argument. (SDK issue 27573)

  • dart:developer

    • Added Service class.
      • Allows inspecting and controlling the VM service protocol HTTP server.
      • Provides an API to access the ID of an Isolate.

Tool changes

  • Dart Dev Compiler

    • Support calls to loadLibrary() on deferred libraries. Deferred libraries are still loaded eagerly. (SDK issue 27343)

1.20.1 - 2016-10-13

Patch release, resolves one issue:

  • Dartium: Fixes a bug that caused crashes. No issue filed.

Strong Mode

  • It is no longer a warning when casting from dynamic to a composite type (SDK issue 27766).

    main() {
      dynamic obj = <int>[1, 2, 3];
      // This is now allowed without a warning.
      List<int> list = obj;

1.20.0 - 2016-10-11

Dart VM

  • We have improved the way that the VM locates the native code library for a native extension (e.g. dart-ext: import). We have updated this article on native extensions to reflect the VM's improved behavior.

  • Linux builds of the VM will now use the tcmalloc library for memory allocation. This has the advantages of better debugging and profiling support and faster small allocations, with the cost of slightly larger initial memory footprint, and slightly slower large allocations.

  • We have improved the way the VM searches for trusted root certificates for secure socket connections on Linux. First, the VM will look for trusted root certificates in standard locations on the file system (/etc/pki/tls/certs/ca-bundle.crt followed by /etc/ssl/certs), and only if these do not exist will it fall back on the builtin trusted root certificates. This behavior can be overridden on Linux with the new flags --root-certs-file and --root-certs-cache. The former is the path to a file containing the trusted root certificates, and the latter is the path to a directory containing root certificate files hashed using c_rehash.

  • The VM now throws a catchable Error when method compilation fails. This allows easier debugging of syntax errors, especially when testing. (SDK issue 23684)

Core library changes

  • dart:core: Remove deprecated Resource class. Use the class in package:resource instead.
  • dart:async
    • Future.wait now catches synchronous errors and returns them in the returned Future. (SDK issue 27249)
    • More aggressively returns a Future on Stream.cancel operations. Discourages to return null from cancel. (SDK issue 26777)
    • Fixes a few bugs where the cancel future wasn't passed through transformations.
  • dart:io
    • Added WebSocket.addUtf8Text to allow sending a pre-encoded text message without a round-trip UTF-8 conversion. (SDK issue 27129)

Strong Mode

  • Breaking change - it is an error if a generic type parameter cannot be inferred (SDK issue 26992).

    class Cup<T> {
      Cup(T t);
    main() {
      // Error because:
      // - if we choose Cup<num> it is not assignable to `cOfInt`,
      // - if we choose Cup<int> then `n` is not assignable to int.
      num n;
      C<int> cOfInt = new C(n);
  • New feature - use @checked to override a method and tighten a parameter type (SDK issue 25578).

    import 'package:meta/meta.dart' show checked;
    class View {
      addChild(View v) {}
    class MyView extends View {
      // this override is legal, it will check at runtime if we actually
      // got a MyView.
      addChild(@checked MyView v) {}
    main() {
      dynamic mv = new MyView();
      mv.addChild(new View()); // runtime error
  • New feature - use @virtual to allow field overrides in strong mode (SDK issue 27384).

    import 'package:meta/meta.dart' show virtual;
    class Base {
      @virtual int x;
    class Derived extends Base {
      int x;
      // Expose the hidden storage slot:
      int get superX => super.x;
      set superX(int v) { super.x = v; }
  • Breaking change - infer list and map literals from the context type as well as their values, consistent with generic methods and instance creation (SDK issue 27151).

    import 'dart:async';
    main() async {
      var b = new Future<B>.value(new B());
      var c = new Future<C>.value(new C());
      var/*infer List<Future<A>>*/ list = [b, c];
      var/*infer List<A>*/ result = await Future.wait(list);
    class A {}
    class B extends A {}
    class C extends A {}

Tool changes

  • dartfmt - upgraded to v0.2.10

    • Don't crash on annotations before parameters with trailing commas.
    • Always split enum declarations if they end in a trailing comma.
    • Add --set-exit-if-changed to set the exit code on a change.
  • Pub

    • Pub no longer generates a packages/ directory by default. Instead, it generates a .packages file, called a package spec. To generate a packages/ directory in addition to the package spec, use the --packages-dir flag with pub get, pub upgrade, and pub downgrade. See the Good-bye symlinks article for details.

1.19.1 - 2016-09-08

Patch release, resolves one issue:

  • Dartdoc: Fixes a bug that prevented generation of docs. (Dartdoc issue 1233)

1.19.0 - 2016-08-26

Language changes

  • The language now allows a trailing comma after the last argument of a call and the last parameter of a function declaration. This can make long argument or parameter lists easier to maintain, as commas can be left as-is when reordering lines. For details, see SDK issue 26644.

Tool Changes

  • dartfmt - upgraded to v0.2.9+1

    • Support trailing commas in argument and parameter lists.
    • Gracefully handle read-only files.
    • About a dozen other bug fixes.
  • Pub

    • Added a --no-packages-dir flag to pub get, pub upgrade, and pub downgrade. When this flag is passed, pub will not generate a packages/ directory, and will remove that directory and any symlinks to it if they exist. Note that this replaces the unsupported --no-package-symlinks flag.

    • Added the ability for packages to declare a constraint on the Flutter SDK:

        flutter: ^0.1.2
        sdk: >=1.19.0 <2.0.0

      A Flutter constraint will only be satisfiable when pub is running in the context of the flutter executable, and when the Flutter SDK version matches the constraint.

    • Added sdk as a new package source that fetches packages from a hard-coded SDK. Currently only the flutter SDK is supported:

          sdk: flutter
          version: ^0.0.1

      A Flutter sdk dependency will only be satisfiable when pub is running in the context of the flutter executable, and when the Flutter SDK contains a package with the given name whose version matches the constraint.

    • tar files on Linux are now created with 0 as the user and group IDs. This fixes a crash when publishing packages while using Active Directory.

    • Fixed a bug where packages from a hosted HTTP URL were considered the same as packages from an otherwise-identical HTTPS URL.

    • Fixed timer formatting for timers that lasted longer than a minute.

    • Eliminate some false negatives when determining whether global executables are on the user's executable path.

  • dart2js

    • dart2dart (aka dart2js --output-type=dart) has been removed (this was deprecated in Dart 1.11).

Dart VM

  • The dependency on BoringSSL has been rolled forward. Going forward, builds of the Dart VM including secure sockets will require a compiler with C++11 support. For details, see the Building wiki page.

Strong Mode

  • New feature - an option to disable implicit casts (SDK issue 26583), see the documentation for usage instructions and examples.

  • New feature - an option to disable implicit dynamic (SDK issue 25573), see the documentation for usage instructions and examples.

  • Breaking change - infer generic type arguments from the constructor invocation arguments (SDK issue 25220).

    var map = new Map<String, String>();
    // infer: Map<String, String>
    var otherMap = new Map.from(map);
  • Breaking change - infer local function return type (SDK issue 26414).

    void main() {
      // infer: return type is int
      f() { return 40; }
      int y = f() + 2; // type checks
  • Breaking change - allow type promotion from a generic type parameter (SDK issue 26414).

    void fn/*<T>*/(/*=T*/ object) {
      if (object is String) {
        // Treat `object` as `String` inside this block.
        // But it will require a cast to pass it to something that expects `T`.
  • Breaking change - smarter inference for Future.then (SDK issue 25944). Previous workarounds that use async/await or .then/*<Future<SomeType>>*/ should no longer be necessary.

    // This will now infer correctly.
    Future<List<int>> t2 = f.then((_) => [3]);
    // This infers too.
    Future<int> t2 = f.then((_) => new Future.value(42));
  • Breaking change - smarter inference for async functions (SDK issue 25322).

    void test() async {
      List<int> x = await [4]; // was previously inferred
      List<int> y = await new Future.value([4]); // now inferred too
  • Breaking change - sideways casts are no longer allowed (SDK issue 26120).

1.18.1 - 2016-08-02

Patch release, resolves two issues and improves performance:

1.18.0 - 2016-07-27

Core library changes

  • dart:core
    • Improved performance when parsing some common URIs.
    • Fixed bug in Uri.resolve (SDK issue 26804).
  • dart:io
    • Adds file locking modes FileLock.BLOCKING_SHARED and FileLock.BLOCKING_EXCLUSIVE.

1.17.1 - 2016-06-10

Patch release, resolves two issues:

1.17.0 - 2016-06-08

Core library changes

  • dart:convert

    • Deprecate ChunkedConverter which was erroneously added in 1.16.
  • dart:core

    • Uri.replace supports iterables as values for the query parameters.
    • Uri.parseIPv6Address returns a Uint8List.
  • dart:io

    • Added NetworkInterface.listSupported, which is true when NetworkInterface.list is supported, and false otherwise. Currently, NetworkInterface.list is not supported on Android.

Tool Changes

  • Pub

    • TAR files created while publishing a package on Mac OS and Linux now use a more portable format.

    • Errors caused by invalid arguments now print the full usage information for the command.

    • SDK constraints for dependency overrides are no longer considered when determining the total SDK constraint for a lockfile.

    • A bug has been fixed in which a lockfile was considered up-to-date when it actually wasn't.

    • A bug has been fixed in which pub get --offline would crash when a prerelease version was selected.

  • Dartium and content shell

    • Debugging Dart code inside iframes improved, was broken.

1.16.1 - 2016-05-24

Patch release, resolves one issue:

  • VM: Fixes a bug that caused intermittent hangs on Windows. (SDK issue 26400)

1.16.0 - 2016-04-26

Core library changes

  • dart:convert

    • Added BASE64URL codec and corresponding Base64Codec.urlSafe constructor.

    • Introduce ChunkedConverter and deprecate chunked methods on Converter.

  • dart:html

    There have been a number of BREAKING changes to align APIs with recent changes in Chrome. These include:

    • Chrome's ShadowRoot interface no longer has the methods getElementById, getElementsByClassName, and getElementsByTagName, e.g.,


      should become:

    • The clipboardData property has been removed from KeyEvent and Event. It has been moved to the new ClipboardEvent class, which is now used by copy, cut, and paste events.

    • The layer property has been removed from KeyEvent and UIEvent. It has been moved to MouseEvent.

    • The Point get page property has been removed from UIEvent. It still exists on MouseEvent and Touch.

    There have also been a number of other additions and removals to dart:html, dart:indexed_db, dart:svg, dart:web_audio, and dart:web_gl that correspond to changes to Chrome APIs between v39 and v45. Many of the breaking changes represent APIs that would have caused runtime exceptions when compiled to Javascript and run on recent Chrome releases.

  • dart:io

    • Added SecurityContext.alpnSupported, which is true if a platform supports ALPN, and false otherwise.

JavaScript interop

For performance reasons, a potentially BREAKING change was added for libraries that use JS interop. Any Dart file that uses @JS annotations on declarations (top-level functions, classes or class members) to interop with JavaScript code will require that the file have the annotation @JS() on a library directive.

library my_library;

The analyzer will enforce this by generating the error:

The @JS() annotation can only be used if it is also declared on the library directive.

If part file uses the @JS() annotation, the library that uses the part should have the @JS() annotation e.g.,

// library_1.dart
library library_1;

import 'package:js/js.dart';

part 'part_1.dart';
// part_1.dart
part of library_1;

external List<FrameworkStabilizer> get frameworkStabilizers;

If your library already has a JS module e.g.,

library my_library;

Then your library will work without any additional changes.


  • Static checking of for in statements. These will now produce static warnings:

    // Not Iterable.
    for (var i in 1234) { ... }
    // String cannot be assigned to int.
    for (int n in <String>["a", "b"]) { ... }

Tool Changes

  • Pub

    • pub serve now provides caching headers that should improve the performance of requesting large files multiple times.

    • Both pub get and pub upgrade now have a --no-precompile flag that disables precompilation of executables and transformed dependencies.

    • pub publish now resolves symlinks when publishing from a Git repository. This matches the behavior it always had when publishing a package that wasn't in a Git repository.

  • Dart Dev Compiler

    • The experimental dartdevc executable has been added to the SDK.

    • It will help early adopters validate the implementation and provide feedback. dartdevc is not yet ready for production usage.

    • Read more about the Dart Dev Compiler here.

1.15.0 - 2016-03-09

Core library changes

  • dart:async

    • Made StreamView class a const class.
  • dart:core

    • Added Uri.queryParametersAll to handle multiple query parameters with the same name.
  • dart:io

    • Added SecurityContext.usePrivateKeyBytes, SecurityContext.useCertificateChainBytes, SecurityContext.setTrustedCertificatesBytes, and SecurityContext.setClientAuthoritiesBytes.
    • Breaking The named directory argument of SecurityContext.setTrustedCertificates has been removed.
    • Added support to SecurityContext for PKCS12 certificate and key containers.
    • All calls in SecurityContext that accept certificate data now accept an optional named parameter password, similar to SecurityContext.usePrivateKeyBytes, for use as the password for PKCS12 data.

Tool changes

  • Dartium and content shell

    • The Chrome-based tools that ship as part of the Dart SDK - Dartium and content shell - are now based on Chrome version 45 (instead of Chrome 39).
    • Dart browser libraries (dart:html, dart:svg, etc) have not been updated.
      • These are still based on Chrome 39.
      • These APIs will be updated in a future release.
    • Note that there are experimental APIs which have changed in the underlying browser, and will not work with the older libraries. For example, Element.animate.
  • dartfmt - upgraded to v0.2.4

    • Better handling for long collections with comments.
    • Always put member metadata annotations on their own line.
    • Indent functions in named argument lists with non-functions.
    • Force the parameter list to split if a split occurs inside a function-typed parameter.
    • Don't force a split for before a single named argument if the argument itself splits.

Service protocol changes

  • Fixed a documentation bug where the field extensionRPCs in Isolate was not marked optional.

Experimental language features

  • Added support for configuration-specific imports. On the VM and dart2js, they can be enabled with --conditional-directives.

    The analyzer requires additional configuration:

        enableConditionalDirectives: true

    Read about configuring the analyzer for more details.

1.14.2 - 2016-02-10

Patch release, resolves three issues:

  • VM: Fixed a code generation bug on x64. (SDK commit 834b3f02)

  • dart:io: Fixed EOF detection when reading some special device files. (SDK issue 25596)

  • Pub: Fixed an error using hosted dependencies in SDK version 1.14. (Pub issue 1386)

1.14.1 - 2016-02-04

Patch release, resolves one issue:

  • Debugger: Fixes a VM crash when a debugger attempts to set a break point during isolate initialization. (SDK issue 25618)

1.14.0 - 2016-01-28

Core library changes

  • dart:async

    • Added Future.any static method.
    • Added Stream.fromFutures constructor.
  • dart:convert

    • Base64Decoder.convert now takes optional start and end parameters.
  • dart:core

    • Added current getter to StackTrace class.
    • Uri class added support for data URIs
      • Added two new constructors: dataFromBytes and dataFromString.
      • Added a data getter for data: URIs with a new UriData class for the return type.
    • Added growable parameter to List.filled constructor.
    • Added microsecond support to DateTime: DateTime.microsecond, DateTime.microsecondsSinceEpoch, and new DateTime.fromMicrosecondsSinceEpoch.
  • dart:math

    • Random added a secure constructor returning a cryptographically secure random generator which reads from the entropy source provided by the embedder for every generated random value.
  • dart:io

    • Platform added a static isIOS getter and Platform.operatingSystem may now return ios.
    • Platform added a static packageConfig getter.
    • Added support for WebSocket compression as standardized in RFC 7692.
    • Compression is enabled by default for all WebSocket connections.
      • The optionally named parameter compression on the methods WebSocket.connect, WebSocket.fromUpgradedSocket, and WebSocketTransformer.upgrade and the WebSocketTransformer constructor can be used to modify or disable compression using the new CompressionOptions class.
  • dart:isolate

    • Added experimental support for Package Resolution Configuration.
      • Added packageConfig and packageRoot instance getters to Isolate.
      • Added a resolvePackageUri method to Isolate.
      • Added named arguments packageConfig and automaticPackageResolution to the Isolate.spawnUri constructor.

Tool changes

  • dartfmt

    • Better line splitting in a variety of cases.

    • Other optimizations and bug fixes.

  • Pub

    • Breaking: Pub now eagerly emits an error when a pubspec's “name” field is not a valid Dart identifier. Since packages with non-identifier names were never allowed to be published, and some of them already caused crashes when being written to a .packages file, this is unlikely to break many people in practice.

    • Breaking: Support for barback versions prior to 0.15.0 (released July

      1. has been dropped. Pub will no longer install these older barback versions.
    • pub serve now GZIPs the assets it serves to make load times more similar to real-world use-cases.

    • pub deps now supports a --no-dev flag, which causes it to emit the dependency tree as it would be if no dev_dependencies were in use. This makes it easier to see your package's dependency footprint as your users will experience it.

    • pub global run now detects when a global executable's SDK constraint is no longer met and errors out, rather than trying to run the executable anyway.

    • Pub commands that check whether the lockfile is up-to-date (pub run, pub deps, pub serve, and pub build) now do additional verification. They ensure that any path dependencies' pubspecs haven't been changed, and they ensure that the current SDK version is compatible with all dependencies.

    • Fixed a crashing bug when using pub global run on a global script that didn't exist.

    • Fixed a crashing bug when a pubspec contains a dependency without a source declared.

1.13.2 - 2016-01-06

Patch release, resolves one issue:

1.13.1 - 2015-12-17

Patch release, resolves three issues:

1.13.0 - 2015-11-18

Core library changes

  • dart:async

    • StreamController added getters for onListen, onPause, and onResume with the corresponding new typedef void ControllerCallback().
    • StreamController added a getter for onCancel with the corresponding new typedef ControllerCancelCallback();
    • StreamTransformer instances created with fromHandlers with no handleError callback now forward stack traces along with errors to the resulting streams.
  • dart:convert

    • Added support for Base-64 encoding and decoding.
      • Added new classes Base64Codec, Base64Encoder, and Base64Decoder.
      • Added new top-level const Base64Codec BASE64.
  • dart:core

    • Uri added removeFragment method.
    • String.allMatches (implementing Pattern.allMatches) is now lazy, as all allMatches implementations are intended to be.
    • Resource is deprecated, and will be removed in a future release.
  • dart:developer

    • Added Timeline class for interacting with Observatory's timeline feature.
    • Added ServiceExtensionHandler, ServiceExtensionResponse, and registerExtension which enable developers to provide their own VM service protocol extensions.
  • dart:html, dart:indexed_db, dart:svg, dart:web_audio, dart:web_gl, dart:web_sql

    • The return type of some APIs changed from double to num. Dartium is now using JS interop for most operations. JS does not distinguish between numeric types, and will return a number as an int if it fits in an int. This will mostly cause an error if you assign to something typed double in checked mode. You may need to insert a toDouble() call or accept num. Examples of APIs that are affected include Element.getBoundingClientRect and TextMetrics.width.
  • dart:io

    • Breaking: Secure networking has changed, replacing the NSS library with the BoringSSL library. SecureSocket, SecureServerSocket, RawSecureSocket,RawSecureServerSocket, HttpClient, and HttpServer now all use a SecurityContext object which contains the certificates and keys used for secure TLS (SSL) networking.

      This is a breaking change for server applications and for some client applications. Certificates and keys are loaded into the SecurityContext from PEM files, instead of from an NSS certificate database. Information about how to change applications that use secure networking is at https://www.dartlang.org/server/tls-ssl.html

    • HttpClient no longer sends URI fragments in the request. This is not allowed by the HTTP protocol. The HttpServer still gracefully receives fragments, but discards them before delivering the request.

    • To allow connections to be accepted on the same port across different isolates, set the shared argument to true when creating server socket and HttpServer instances.

      • The deprecated ServerSocketReference and RawServerSocketReference classes have been removed.
      • The corresponding reference properties on ServerSocket and RawServerSocket have been removed.
  • dart:isolate

    • spawnUri added an environment named argument.

Tool changes

  • dart2js and Dartium now support improved Javascript Interoperability via the js package.

  • docgen and dartdocgen no longer ship in the SDK. The docgen sources have been removed from the repository.

  • This is the last release to ship the VM's “legacy debug protocol”. We intend to remove the legacy debug protocol in Dart VM 1.14.

  • The VM's Service Protocol has been updated to version 3.0 to take care of a number of issues uncovered by the first few non-observatory clients. This is a potentially breaking change for clients.

  • Dartium has been substantially changed. Rather than using C++ calls into Chromium internals for DOM operations it now uses JS interop. The DOM objects in dart:html and related libraries now wrap a JavaScript object and delegate operations to it. This should be mostly transparent to users. However, performance and memory characteristics may be different from previous versions. There may be some changes in which DOM objects are wrapped as Dart objects. For example, if you get a reference to a Window object, even through JS interop, you will always see it as a Dart Window, even when used cross-frame. We expect the change to using JS interop will make it much simpler to update to new Chrome versions.

1.12.2 - 2015-10-21

Core library changes

  • dart:io

    • A memory leak in creation of Process objects is fixed.

1.12.1 - 2015-09-08

Tool changes

  • Pub

    • Pub will now respect .gitignore when validating a package before it's published. For example, if a LICENSE file exists but is ignored, that is now an error.

    • If the package is in a subdirectory of a Git repository and the entire subdirectory is ignored with .gitignore, pub will act as though nothing was ignored instead of uploading an empty package.

    • The heuristics for determining when pub get needs to be run before various commands have been improved. There should no longer be false positives when non-dependency sections of the pubspec have been modified.

1.12.0 - 2015-08-31

Language changes

  • Null-aware operators
    • ??: if null operator. expr1 ?? expr2 evaluates to expr1 if not null, otherwise expr2.
    • ??=: null-aware assignment. v ??= expr causes v to be assigned expr only if v is null.
    • x?.p: null-aware access. x?.p evaluates to x.p if x is not null, otherwise evaluates to null.
    • x?.m(): null-aware method invocation. x?.m() invokes m only if x is not null.

Core library changes

  • dart:async

    • StreamController added setters for the onListen, onPause, onResume and onCancel callbacks.
  • dart:convert

    • LineSplitter added a split static method returning an Iterable.
  • dart:core

    • Uri class now perform path normalization when a URI is created. This removes most .. and . sequences from the URI path. Purely relative paths (no scheme or authority) are allowed to retain some leading “dot” segments. Also added hasAbsolutePath, hasEmptyPath, and hasScheme properties.
  • dart:developer

    • New log function to transmit logging events to Observatory.
  • dart:html

    • NodeTreeSanitizer added the const trusted field. It can be used instead of defining a NullTreeSanitizer class when calling setInnerHtml or other methods that create DOM from text. It is also more efficient, skipping the creation of a DocumentFragment.
  • dart:io

    • Added two new file modes, WRITE_ONLY and WRITE_ONLY_APPEND for opening a file write only. eaeecf2
    • Change stdout/stderr to binary mode on Windows. 4205b29
  • dart:isolate

    • Added onError, onExit and errorsAreFatal parameters to Isolate.spawnUri.
  • dart:mirrors

    • InstanceMirror.delegate moved up to ObjectMirror.
    • Fix InstanceMirror.getField optimization when the selector is an operator.
    • Fix reflective NoSuchMethodErrors to match their non-reflective counterparts when due to argument mismatches. (VM only)

Tool changes

  • Documentation tools

    • dartdoc is now the default tool to generate static HTML for API docs. Learn more.

    • docgen and dartdocgen have been deprecated. Currently plan is to remove them in 1.13.

  • Formatter (dartfmt)

    • Over 50 bugs fixed.

    • Optimized line splitter is much faster and produces better output on complex code.

  • Observatory

    • Allocation profiling.

    • New feature to display output from logging.

    • Heap snapshot analysis works for 64-bit VMs.

    • Improved ability to inspect typed data, regex and compiled code.

    • Ability to break on all or uncaught exceptions from Observatory's debugger.

    • Ability to set closure-specific breakpoints.

    • ‘anext’ - step past await/yield.

    • Preserve when a variable has been expanded/unexpanded in the debugger.

    • Keep focus on debugger input box whenever possible.

    • Echo stdout/stderr in the Observatory debugger. Standalone-only so far.

    • Minor fixes to service protocol documentation.

  • Pub

    • Breaking: various commands that previously ran pub get implicitly no longer do so. Instead, they merely check to make sure the “.packages” file is newer than the pubspec and the lock file, and fail if it's not.

    • Added support for --verbosity=error and --verbosity=warning.

    • pub serve now collapses multiple GET requests into a single line of output. For full output, use --verbose.

    • pub deps has improved formatting for circular dependencies on the entrypoint package.

    • pub run and pub global run

      • Breaking: to match the behavior of the Dart VM, executables no longer run in checked mode by default. A --checked flag has been added to run them in checked mode manually.

      • Faster start time for executables that don't import transformed code.

      • Binstubs for globally-activated executables are now written in the system encoding, rather than always in UTF-8. To update existing executables, run pub cache repair.

    • pub get and pub upgrade

      • Pub will now generate a “.packages” file in addition to the “packages” directory when running pub get or similar operations, per the package spec proposal. Pub now has a --no-package-symlinks flag that will stop “packages” directories from being generated at all.

      • An issue where HTTP requests were sometimes made even though --offline was passed has been fixed.

      • A bug with --offline that caused an unhelpful error message has been fixed.

      • Pub will no longer time out when a package takes a long time to download.

    • pub publish

      • Pub will emit a non-zero exit code when it finds a violation while publishing.

      • .gitignore files will be respected even if the package isn't at the top level of the Git repository.

    • Barback integration

      • A crashing bug involving transformers that only apply to non-public code has been fixed.

      • A deadlock caused by declaring transformer followed by a lazy transformer (such as the built-in $dart2js transformer) has been fixed.

      • A stack overflow caused by a transformer being run multiple times on the package that defines it has been fixed.

      • A transformer that tries to read a non-existent asset in another package will now be re-run if that asset is later created.

VM Service Protocol Changes

  • BREAKING The service protocol now sends JSON-RPC 2.0-compatible server-to-client events. To reflect this, the service protocol version is now 2.0.

  • The service protocol now includes a "jsonrpc" property in its responses, as opposed to "json-rpc".

  • The service protocol now properly handles requests with non-string ids. Numeric ids are no longer converted to strings, and null ids now don't produce a response.

  • Some RPCs that didn't include a "jsonrpc" property in their responses now include one.

1.11.2 - 2015-08-03

Core library changes

  • Fix a bug where WebSocket.close() would crash if called after WebSocket.cancel().

1.11.1 - 2015-07-02

Tool changes

  • Pub will always load Dart SDK assets from the SDK whose pub executable was run, even if a DART_SDK environment variable is set.

1.11.0 - 2015-06-25

Core library changes

  • dart:core

    • Iterable added an empty constructor. dcf0286
    • Iterable can now be extended directly. An alternative to extending IterableBase from dart:collection.
    • List added an unmodifiable constructor. r45334
    • Map added an unmodifiable constructor. r45733
    • int added a gcd method. a192ef4
    • int added a modInverse method. f6f338c
    • StackTrace added a fromString constructor. 68dd6f6
    • Uri added a directory constructor. d8dbb4a
    • List iterators may not throw ConcurrentModificationError as eagerly in release mode. In checked mode, the modification check is still as eager as possible. r45198
  • dart:developer - NEW

    • Replaces the deprecated dart:profiler library.
    • Adds new functions debugger and inspect. 6e42aec
  • dart:io

    • FileSystemEntity added a uri property. 8cf32dc
    • Platform added a static resolvedExecutable property. c05c8c6
  • dart:html

    • Element methods, appendHtml and insertAdjacentHtml now take nodeValidator and treeSanitizer parameters, and the inputs are consistently sanitized. r45818 announcement
  • dart:isolate

    • BREAKING The positional priority parameter of Isolate.ping and Isolate.kill is now a named parameter named priority.
    • BREAKING Removed the Isolate.AS_EVENT priority.
    • Isolate methods ping and addOnExitListener now have a named parameter response. r45092
    • Isolate.spawnUri added a named argument checked.
    • Remove the experimental state of the API.
  • dart:profiler - DEPRECATED

    • This library will be removed in 1.12. Use dart:developer instead.

Tool changes

  • This is the first release that does not include the Eclipse-based Dart Editor. See dartlang.org/tools for alternatives.
  • This is the last release that ships the (unsupported) dart2dart (aka dart2js --output-type=dart) utility as part of dart2js

1.10.0 - 2015-04-29

Core library changes

  • dart:convert

    • POTENTIALLY BREAKING Fix behavior of HtmlEscape. It no longer escapes no-break space (U+00A0) anywhere or forward slash (/, U+002F) in element context. Slash is still escaped using HtmlEscapeMode.UNKNOWN. r45003, r45153, r45189
  • dart:core

    • Uri.parse added start and end positional arguments.
  • dart:html

    • POTENTIALLY BREAKING CssClassSet method arguments must now be ‘tokens’, i.e. non-empty strings with no white-space characters. The implementation was incorrect for class names containing spaces. The fix is to forbid spaces and provide a faster implementation. Announcement
  • dart:io

    • ProcessResult now exposes a constructor.
    • import and Isolate.spawnUri now supports the Data URI scheme on the VM.

Tool Changes


  • Running pub run foo within a package now runs the foo executable defined by the foo package. The previous behavior ran bin/foo. This makes it easy to run binaries in dependencies, for instance pub run test.

  • On Mac and Linux, signals sent to pub run and forwarded to the child command.

1.9.3 - 2015-04-14

This is a bug fix release which merges a number of commits from bleeding_edge.

  • dart2js: Addresses as issue with minified Javascript output with CSP enabled - r44453

  • Editor: Fixes accidental updating of files in the pub cache during rename refactoring - r44677

  • Editor: Fix for issue 23032 regarding skipped breakpoints on Windows - r44824

  • dart:mirrors: Fix MethodMirror.source when the method is on the first line in a script - r44957, r44976

  • pub: Fix for issue 23084: Pub can fail to load transformers necessary for local development - r44876

1.9.1 - 2015-03-25

Language changes

  • Support for async, await, sync*, async*, yield, yield*, and await for. See the the language tour for more details.

  • Enum support is fully enabled. See the language tour for more details.

Tool changes

  • The formatter is much more comprehensive and generates much more readable code. See its tool page for more details.

  • The analysis server is integrated into the IntelliJ plugin and the Dart editor. This allows analysis to run out-of-process, so that interaction remains smooth even for large projects.

  • Analysis supports more and better hints, including unused variables and unused private members.

Core library changes


  • There's a new model for shared server sockets with no need for a Socket reference.

  • A new, much faster regular expression engine.

  • The Isolate API now works across the VM and dart2js.


For more information on any of these changes, see the corresponding documentation on the Dart API site.

  • dart:async:

    • Future.wait added a new named argument, cleanUp, which is a callback that releases resources allocated by a successful Future.

    • The SynchronousStreamController class was added as an explicit name for the type returned when the sync argument is passed to new StreamController.

  • dart:collection: The new SplayTreeSet.from(Iterable) constructor was added.

  • dart:convert: Utf8Encoder.convert and Utf8Decoder.convert added optional start and end arguments.

  • dart:core:

    • RangeError added new static helper functions: checkNotNegative, checkValidIndex, checkValidRange, and checkValueInInterval.

    • int added the modPow function.

    • String added the replaceFirstMapped and replaceRange functions.

  • dart:io:

    • Support for locking files to prevent concurrent modification was added. This includes the File.lock, File.lockSync, File.unlock, and File.unlockSync functions as well as the FileLock class.

    • Support for starting detached processes by passing the named mode argument (a ProcessStartMode) to Process.start. A process can be fully attached, fully detached, or detached except for its standard IO streams.

    • HttpServer.bind and HttpServer.bindSecure added the v6Only named argument. If this is true, only IPv6 connections will be accepted.

    • HttpServer.bind, HttpServer.bindSecure, ServerSocket.bind, RawServerSocket.bind, SecureServerSocket.bind and RawSecureServerSocket.bind added the shared named argument. If this is true, multiple servers or sockets in the same Dart process may bind to the same address, and incoming requests will automatically be distributed between them.

    • Deprecation: the experimental ServerSocketReference and RawServerSocketReference classes, as well as getters that returned them, are marked as deprecated. The shared named argument should be used instead. These will be removed in Dart 1.10.

    • Socket.connect and RawSocket.connect added the sourceAddress named argument, which specifies the local address to bind when making a connection.

    • The static Process.killPid method was added to kill a process with a given PID.

    • Stdout added the nonBlocking instance property, which returns a non-blocking IOSink that writes to standard output.

  • dart:isolate:

    • The static getter Isolate.current was added.

    • The Isolate methods addOnExitListener, removeOnExitListener, setErrorsFatal, addOnErrorListener, and removeOnErrorListener now work on the VM.

    • Isolates spawned via Isolate.spawn now allow most objects, including top-level and static functions, to be sent between them.

1.8.5 - 2015-01-21

  • Code generation for SIMD on ARM and ARM64 is fixed.

  • A possible crash on MIPS with newer GCC toolchains has been prevented.

  • A segfault when using rethrow was fixed (issue 21795).

1.8.3 - 2014-12-10

  • Breakpoints can be set in the Editor using file suffixes (issue 21280).

  • IPv6 addresses are properly handled by HttpClient in dart:io, fixing a crash in pub (issue 21698).

  • Issues with the experimental async/await syntax have been fixed.

  • Issues with a set of number operations in the VM have been fixed.

  • ListBase in dart:collection always returns an Iterable with the correct type argument.

1.8.0 - 2014-11-28

  • dart:collection: SplayTree added the toSet function.

  • dart:convert: The JsonUtf8Encoder class was added.

  • dart:core:

    • The IndexError class was added for errors caused by an index being outside its expected range.

    • The new RangeError.index constructor was added. It forwards to new IndexError.

    • RangeError added three new properties. invalidProperty is the value that caused the error, and start and end are the minimum and maximum values that the value is allowed to assume.

    • new RangeError.value and new RangeError.range added an optional message argument.

    • The new String.fromCharCodes constructor added optional start and end arguments.

  • dart:io:

    • Support was added for the Application-Layer Protocol Negotiation extension to the TLS protocol for both the client and server.

    • SecureSocket.connect, SecureServerSocket.bind, RawSecureSocket.connect, RawSecureSocket.secure, RawSecureSocket.secureServer, and RawSecureServerSocket.bind added a supportedProtocols named argument for protocol negotiation.

    • RawSecureServerSocket added a supportedProtocols field.

    • RawSecureSocket and SecureSocket added a selectedProtocol field which contains the protocol selected during protocol negotiation.

1.7.0 - 2014-10-15

Tool changes

  • pub now generates binstubs for packages that are globally activated so that they can be put on the user's PATH and used as normal executables. See the pub global activate documentation.

  • When using dart2js, deferred loading now works with multiple Dart apps on the same page.

Core library changes

  • dart:async: Zone, ZoneDelegate, and ZoneSpecification added the errorCallback function, which allows errors that have been programmatically added to a Future or Stream to be intercepted.

  • dart:io:

    • Breaking change: HttpClient.close must be called for all clients or they will keep the Dart process alive until they time out. This fixes the handling of persistent connections. Previously, the client would shut down immediately after a request.

    • Breaking change: HttpServer no longer compresses all traffic by default. The new autoCompress property can be set to true to re-enable compression.

  • dart:isolate: Isolate.spawnUri added the optional packageRoot argument, which controls how it resolves package: URIs.