sdk/lib/_internal/js_runtime/lib/interceptors.dart - sdk - Git at Google

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.

 library _interceptors;

 import 'dart:_js_embedded_names'
     show DISPATCH_PROPERTY_NAME, TYPE_TO_INTERCEPTOR_MAP;

 import 'dart:collection' hide LinkedList, LinkedListEntry;
 import 'dart:_internal' hide Symbol;
 import "dart:_internal" as _symbol_dev show Symbol;
 import 'dart:_js_helper'
     show
         allMatchesInStringUnchecked,
         JSSyntaxRegExp,
         Primitives,
         argumentErrorValue,
         checkBool,
         checkInt,
         checkNull,
         checkNum,
         checkString,
         defineProperty,
         diagnoseIndexError,
         getIsolateAffinityTag,
         getRuntimeType,
         initNativeDispatch,
         initNativeDispatchFlag,
         regExpGetNative,
         regExpCaptureCount,
         stringContainsUnchecked,
         stringIndexOfStringUnchecked,
         stringLastIndexOfUnchecked,
         stringReplaceAllFuncUnchecked,
         stringReplaceAllUnchecked,
         stringReplaceFirstUnchecked,
         stringReplaceFirstMappedUnchecked,
         stringReplaceRangeUnchecked,
         stringSplitUnchecked,
         throwConcurrentModificationError,
         lookupAndCacheInterceptor,
         StringMatch,
         firstMatchAfter,
         NoInline;

 import 'dart:_foreign_helper'
     show
         getInterceptor,
         JS,
         JS_EFFECT,
         JS_EMBEDDED_GLOBAL,
         JS_INTERCEPTOR_CONSTANT,
         JS_STRING_CONCAT;
 import 'dart:math' show Random;

 part 'js_array.dart';
 part 'js_number.dart';
 part 'js_string.dart';

 final String DART_CLOSURE_PROPERTY_NAME =
     getIsolateAffinityTag(r'_$dart_dartClosure');

 String _symbolToString(Symbol symbol) => _symbol_dev.Symbol.getName(symbol);

 _symbolMapToStringMap(Map<Symbol, dynamic> map) {
   if (map == null) return null;
   var result = new Map<String, dynamic>();
   map.forEach((Symbol key, value) {
     result[_symbolToString(key)] = value;
   });
   return result;
 }

 getDispatchProperty(object) {
   return JS(
       '', '#[#]', object, JS_EMBEDDED_GLOBAL('String', DISPATCH_PROPERTY_NAME));
 }

 setDispatchProperty(object, value) {
   defineProperty(
       object, JS_EMBEDDED_GLOBAL('String', DISPATCH_PROPERTY_NAME), value);
 }

 // Avoid inlining this method because inlining gives us multiple allocation
 // points for records which is bad because it leads to polymorphic access.
 @NoInline()
 makeDispatchRecord(interceptor, proto, extension, indexability) {
   // Dispatch records are stored in the prototype chain, and in some cases, on
   // instances.
   //
   // The record layout and field usage is designed to minimize the number of
   // operations on the common paths.
   //
   // [interceptor] is the interceptor - a holder of methods for the object,
   // i.e. the prototype of the interceptor class.
   //
   // [proto] is usually the prototype, used to check that the dispatch record
   // matches the object and is not the dispatch record of a superclass.  Other
   // values:
   //  - `false` for leaf classes that need no check.
   //  - `true` for Dart classes where the object is its own interceptor (unused)
   //  - a function used to continue matching.
   //
   // [extension] is used for irregular cases.
   //
   // [indexability] is used to cache whether or not the object
   // implements JavaScriptIndexingBehavior.
   //
   //     proto  interceptor extension action
   //     -----  ----------- --------- ------
   //     false  I                     use interceptor I
   //     true   -                     use object
   //     P      I                     if object's prototype is P, use I
   //     F      -           P         if object's prototype is P, call F

   return JS('', '{i: #, p: #, e: #, x: #}', interceptor, proto, extension,
       indexability);
 }

 dispatchRecordInterceptor(record) => JS('', '#.i', record);
 dispatchRecordProto(record) => JS('', '#.p', record);
 dispatchRecordExtension(record) => JS('', '#.e', record);
 dispatchRecordIndexability(record) => JS('bool|Null', '#.x', record);

 /**
  * Returns the interceptor for a native class instance. Used by
  * [getInterceptor].
  */
 getNativeInterceptor(object) {
   var record = getDispatchProperty(object);

   if (record == null) {
     if (initNativeDispatchFlag == null) {
       initNativeDispatch();
       record = getDispatchProperty(object);
     }
   }

   if (record != null) {
     var proto = dispatchRecordProto(record);
     if (false == proto) return dispatchRecordInterceptor(record);
     if (true == proto) return object;
     var objectProto = JS('', 'Object.getPrototypeOf(#)', object);
     if (JS('bool', '# === #', proto, objectProto)) {
       return dispatchRecordInterceptor(record);
     }

     var extension = dispatchRecordExtension(record);
     if (JS('bool', '# === #', extension, objectProto)) {
       // TODO(sra): The discriminator returns a tag.  The tag is an uncached or
       // instance-cached tag, defaulting to instance-cached if caching
       // unspecified.
       var discriminatedTag = JS('', '(#)(#, #)', proto, object, record);
       throw new UnimplementedError('Return interceptor for $discriminatedTag');
     }
   }

   // Check for cached UnknownJavaScriptObject. This avoids doing the slow
   // dispatch-record based lookup for repeated js-interop classes.
   var constructor = JS('', '#.constructor', object);
   var interceptor = lookupInterceptorByConstructor(constructor);
   if (interceptor != null) return interceptor;

   // This takes care of dispatch-record based caching, but not constructor based
   // caching of [UnknownJavaScriptObject]s.
   interceptor = lookupAndCacheInterceptor(object);
   if (interceptor != null) return interceptor;

   // JavaScript Objects created via object literals and `Object.create(null)`
   // are 'plain' Objects.  This test could be simplified and the dispatch path
   // be faster if Object.prototype was pre-patched with a non-leaf dispatch
   // record.
   if (JS('bool', 'typeof # == "function"', object)) {
     interceptor = JS_INTERCEPTOR_CONSTANT(JavaScriptFunction);
     // TODO(sra): Investigate caching on `Function`. It might be impossible if
     // some HTML embedded objects on some browsers are (still) JS functions.
     return interceptor;
   }
   var proto = JS('', 'Object.getPrototypeOf(#)', object);
   if (JS('bool', '# == null', proto)) {
     // Nowhere to cache output.
     return JS_INTERCEPTOR_CONSTANT(PlainJavaScriptObject);
   }
   interceptor = JS_INTERCEPTOR_CONSTANT(UnknownJavaScriptObject);
   if (JS('bool', '# === Object.prototype', proto)) {
     interceptor = JS_INTERCEPTOR_CONSTANT(PlainJavaScriptObject);
     // TODO(sra): Investigate caching on 'Object'. It might be impossible if
     // some native class is plain Object (e.g. like Firefox's ImageData).
     return interceptor;
   }
   if (JS('bool', 'typeof # == "function"', constructor)) {
     cacheInterceptorOnConstructor(constructor, interceptor);
     return interceptor;
   }
   return JS_INTERCEPTOR_CONSTANT(UnknownJavaScriptObject);
 }

 // A JS String or Symbol.
 final JS_INTEROP_INTERCEPTOR_TAG = getIsolateAffinityTag(r'_$dart_js');

 lookupInterceptorByConstructor(constructor) {
   return constructor == null
       ? null
       : JS('', '#[#]', constructor, JS_INTEROP_INTERCEPTOR_TAG);
 }

 void cacheInterceptorOnConstructor(constructor, interceptor) {
   defineProperty(constructor, JS_INTEROP_INTERCEPTOR_TAG, interceptor);
 }

 var constructorToInterceptor =
     JS('', 'typeof(self.WeakMap) == "undefined" ? new Map() : new WeakMap()');

 XlookupInterceptorByConstructor(constructor) {
   return JS('', '#.get(#)', constructorToInterceptor, constructor);
 }

 void XcacheInterceptorOnConstructor(constructor, interceptor) {
   JS('', '#.set(#, #)', constructorToInterceptor, constructor, interceptor);
 }

 /**
  * Data structure used to map a [Type] to the [Interceptor] and constructors for
  * that type.  It is JavaScript array of 3N entries of adjacent slots containing
  * a [Type], followed by an [Interceptor] class for the type, followed by a
  * JavaScript object map for the constructors.
  *
  * The value of this variable is set by the compiler and contains only types
  * that are user extensions of native classes where the type occurs as a
  * constant in the program.
  *
  * The compiler, in CustomElementsAnalysis, assumes that [typeToInterceptorMap]
  * is accessed only by code that also calls [findIndexForWebComponentType].  If
  * this assumption is invalidated, the compiler will have to be updated.
  */
 get typeToInterceptorMap {
   return JS_EMBEDDED_GLOBAL('', TYPE_TO_INTERCEPTOR_MAP);
 }

 int findIndexForNativeSubclassType(Type type) {
   if (JS('bool', '# == null', typeToInterceptorMap)) return null;
   List map = JS('JSFixedArray', '#', typeToInterceptorMap);
   for (int i = 0; i + 1 < map.length; i += 3) {
     if (type == map[i]) {
       return i;
     }
   }
   return null;
 }

 findInterceptorConstructorForType(Type type) {
   var index = findIndexForNativeSubclassType(type);
   if (index == null) return null;
   List map = JS('JSFixedArray', '#', typeToInterceptorMap);
   return map[index + 1];
 }

 /**
  * Returns a JavaScript function that runs the constructor on its argument, or
  * `null` if there is no such constructor.
  *
  * The returned function takes one argument, the web component object.
  */
 findConstructorForNativeSubclassType(Type type, String name) {
   var index = findIndexForNativeSubclassType(type);
   if (index == null) return null;
   List map = JS('JSFixedArray', '#', typeToInterceptorMap);
   var constructorMap = map[index + 2];
   var constructorFn = JS('', '#[#]', constructorMap, name);
   return constructorFn;
 }

 findInterceptorForType(Type type) {
   var constructor = findInterceptorConstructorForType(type);
   if (constructor == null) return null;
   return JS('', '#.prototype', constructor);
 }

 /**
  * The base interceptor class.
  *
  * The code `r.foo(a)` is compiled to `getInterceptor(r).foo$1(r, a)`.  The
  * value returned by [getInterceptor] holds the methods separately from the
  * state of the instance.  The compiler converts the methods on an interceptor
  * to take the Dart `this` argument as an explicit `receiver` argument.  The
  * JavaScript `this` parameter is bound to the interceptor.
  *
  * In order to have uniform call sites, if a method is defined on an
  * interceptor, methods of that name on plain unintercepted classes also use the
  * interceptor calling convention.  The plain classes are _self-interceptors_,
  * and for them, `getInterceptor(r)` returns `r`.  Methods on plain
  * unintercepted classes have a redundant `receiver` argument and, to enable
  * some optimizations, must ignore `receiver` in favour of `this`.
  *
  * In the case of mixins, a method may be placed on both an intercepted class
  * and an unintercepted class.  In this case, the method must use the `receiver`
  * parameter.
  *
  *
  * There are various optimizations of the general call pattern.
  *
  * When the interceptor can be statically determined, it can be used directly:
  *
  *     CONSTANT_INTERCEPTOR.foo$1(r, a)
  *
  * If there are only a few classes, [getInterceptor] can be specialized with a
  * more efficient dispatch:
  *
  *     getInterceptor$specialized(r).foo$1(r, a)
  *
  * If it can be determined that the receiver is an unintercepted class, it can
  * be called directly:
  *
  *     r.foo$1(r, a)
  *
  * If, further, it is known that the call site cannot call a foo that is
  * mixed-in to a native class, then it is known that the explicit receiver is
  * ignored, and space-saving dummy value can be passed instead:
  *
  *     r.foo$1(0, a)
  *
  * This class defines implementations of *all* methods on [Object] so no
  * interceptor inherits an implementation from [Object].  This enables the
  * implementations on Object to ignore the explicit receiver argument, which
  * allows dummy receiver optimization.
  */
 abstract class Interceptor {
   const Interceptor();

   bool operator ==(other) => identical(this, other);

   int get hashCode => Primitives.objectHashCode(this);

   String toString() => Primitives.objectToHumanReadableString(this);

   // [Interceptor.noSuchMethod] is identical to [Object.noSuchMethod].  However,
   // each copy is compiled differently.  The presence of the method on an
   // Interceptor class forces [noSuchMethod] to use interceptor calling
   // convention.  In the [Interceptor] version, `this` is the explicit receiver
   // argument. In the [Object] version, as Object is not an intercepted class,
   // `this` is the JavaScript receiver, and the explicit receiver is ignored.
   // The noSuchMethod stubs for selectors that use the interceptor calling
   // convention do not know the calling convention and forward `this` and
   // `receiver` to one of these noSuchMethod implementations which selects the
   // correct Dart receiver.
   //
   // We don't allow [noSuchMethod] on intercepted classes (that would force all
   // calls to use interceptor calling convention).  If we did allow it, the
   // interceptor context would select the correct `this`.
   dynamic noSuchMethod(Invocation invocation) {
     throw new NoSuchMethodError(this, invocation.memberName,
         invocation.positionalArguments, invocation.namedArguments);
   }

   Type get runtimeType => getRuntimeType(this);
 }

 /**
  * The interceptor class for [bool].
  */
 class JSBool extends Interceptor implements bool {
   const JSBool();

   // Note: if you change this, also change the function [S].
   String toString() => JS('String', r'String(#)', this);

   bool operator &(bool other) => JS('bool', "# && #", checkBool(other), this);

   bool operator |(bool other) => JS('bool', "# || #", checkBool(other), this);

   bool operator ^(bool other) => !identical(this, checkBool(other));

   // The values here are SMIs, co-prime and differ about half of the bit
   // positions, including the low bit, so they are different mod 2^k.
   int get hashCode => this ? (2 * 3 * 23 * 3761) : (269 * 811);

   Type get runtimeType => bool;
 }

 /**
  * The interceptor class for [Null].
  *
  * This class defines implementations for *all* methods on [Object] since
  * the methods on Object assume the receiver is non-null.  This means that
  * JSNull will always be in the interceptor set for methods defined on Object.
  */
 class JSNull extends Interceptor implements Null {
   const JSNull();

   bool operator ==(other) => identical(null, other);

   // Note: if you change this, also change the function [S].
   String toString() => 'null';

   int get hashCode => 0;

   // The spec guarantees that `null` is the singleton instance of the `Null`
   // class. In the mirrors library we also have to patch the `type` getter to
   // special case `null`.
   Type get runtimeType => Null;

   dynamic noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
 }

 /**
  * The supertype for JSString and JSArray. Used by the backend as to
  * have a type mask that contains the objects that we can use the
  * native JS [] operator and length on.
  */
 abstract class JSIndexable<E> {
   int get length;
   E operator [](int index);
 }

 /**
  * The supertype for JSMutableArray and
  * JavaScriptIndexingBehavior. Used by the backend to have a type mask
  * that contains the objects we can use the JS []= operator on.
  */
 abstract class JSMutableIndexable<E> extends JSIndexable<E> {
   operator []=(int index, E value);
 }

 /**
  * The interface implemented by JavaScript objects.  These are methods in
  * addition to the regular Dart Object methods like [Object.hashCode].
  *
  * This is the type that should be exported by a JavaScript interop library.
  */
 abstract class JSObject {}

 /**
  * Interceptor base class for JavaScript objects not recognized as some more
  * specific native type.
  */
 class JavaScriptObject extends Interceptor implements JSObject {
   const JavaScriptObject();

   // It would be impolite to stash a property on the object.
   int get hashCode => 0;

   Type get runtimeType => JSObject;

   /**
    * Returns the result of the JavaScript objects `toString` method.
    */
   String toString() => JS('String', 'String(#)', this);
 }

 /**
  * Interceptor for plain JavaScript objects created as JavaScript object
  * literals or `new Object()`.
  */
 class PlainJavaScriptObject extends JavaScriptObject {
   const PlainJavaScriptObject();
 }

 /**
  * Interceptor for unclassified JavaScript objects, typically objects with a
  * non-trivial prototype chain.
  *
  * This class also serves as a fallback for unknown JavaScript exceptions.
  */
 class UnknownJavaScriptObject extends JavaScriptObject {
   const UnknownJavaScriptObject();
 }

 /**
  * Interceptor for JavaScript function objects and Dart functions that have
  * been converted to JavaScript functions.
  * These interceptor methods are not always used as the JavaScript function
  * object has also been mangled to support Dart function calling conventions.
  */
 class JavaScriptFunction extends JavaScriptObject implements Function {
   const JavaScriptFunction();

   String toString() {
     var dartClosure = JS('', '#.#', this, DART_CLOSURE_PROPERTY_NAME);
     if (dartClosure == null) return super.toString();
     return 'JavaScript function for ${dartClosure.toString()}';
   }
 }
	// Copyright (c) 2012, the Dart project authors. Please see the AUTHORS file
	// for details. All rights reserved. Use of this source code is governed by a
	// BSD-style license that can be found in the LICENSE file.

	library _interceptors;

	import 'dart:_js_embedded_names'
	show DISPATCH_PROPERTY_NAME, TYPE_TO_INTERCEPTOR_MAP;

	import 'dart:collection' hide LinkedList, LinkedListEntry;
	import 'dart:_internal' hide Symbol;
	import "dart:_internal" as _symbol_dev show Symbol;
	import 'dart:_js_helper'
	show
	allMatchesInStringUnchecked,
	JSSyntaxRegExp,
	Primitives,
	argumentErrorValue,
	checkBool,
	checkInt,
	checkNull,
	checkNum,
	checkString,
	defineProperty,
	diagnoseIndexError,
	getIsolateAffinityTag,
	getRuntimeType,
	initNativeDispatch,
	initNativeDispatchFlag,
	regExpGetNative,
	regExpCaptureCount,
	stringContainsUnchecked,
	stringIndexOfStringUnchecked,
	stringLastIndexOfUnchecked,
	stringReplaceAllFuncUnchecked,
	stringReplaceAllUnchecked,
	stringReplaceFirstUnchecked,
	stringReplaceFirstMappedUnchecked,
	stringReplaceRangeUnchecked,
	stringSplitUnchecked,
	throwConcurrentModificationError,
	lookupAndCacheInterceptor,
	StringMatch,
	firstMatchAfter,
	NoInline;

	import 'dart:_foreign_helper'
	show
	getInterceptor,
	JS,
	JS_EFFECT,
	JS_EMBEDDED_GLOBAL,
	JS_INTERCEPTOR_CONSTANT,
	JS_STRING_CONCAT;
	import 'dart:math' show Random;

	part 'js_array.dart';
	part 'js_number.dart';
	part 'js_string.dart';

	final String DART_CLOSURE_PROPERTY_NAME =
	getIsolateAffinityTag(r'_$dart_dartClosure');

	String _symbolToString(Symbol symbol) => _symbol_dev.Symbol.getName(symbol);

	_symbolMapToStringMap(Map<Symbol, dynamic> map) {
	if (map == null) return null;
	var result = new Map<String, dynamic>();
	map.forEach((Symbol key, value) {
	result[_symbolToString(key)] = value;
	});
	return result;
	}

	getDispatchProperty(object) {
	return JS(
	'', '#[#]', object, JS_EMBEDDED_GLOBAL('String', DISPATCH_PROPERTY_NAME));
	}

	setDispatchProperty(object, value) {
	defineProperty(
	object, JS_EMBEDDED_GLOBAL('String', DISPATCH_PROPERTY_NAME), value);
	}

	// Avoid inlining this method because inlining gives us multiple allocation
	// points for records which is bad because it leads to polymorphic access.
	@NoInline()
	makeDispatchRecord(interceptor, proto, extension, indexability) {
	// Dispatch records are stored in the prototype chain, and in some cases, on
	// instances.
	//
	// The record layout and field usage is designed to minimize the number of
	// operations on the common paths.
	//
	// [interceptor] is the interceptor - a holder of methods for the object,
	// i.e. the prototype of the interceptor class.
	//
	// [proto] is usually the prototype, used to check that the dispatch record
	// matches the object and is not the dispatch record of a superclass. Other
	// values:
	// - `false` for leaf classes that need no check.
	// - `true` for Dart classes where the object is its own interceptor (unused)
	// - a function used to continue matching.
	//
	// [extension] is used for irregular cases.
	//
	// [indexability] is used to cache whether or not the object
	// implements JavaScriptIndexingBehavior.
	//
	// proto interceptor extension action
	// ----- ----------- --------- ------
	// false I use interceptor I
	// true - use object
	// P I if object's prototype is P, use I
	// F - P if object's prototype is P, call F

	return JS('', '{i: #, p: #, e: #, x: #}', interceptor, proto, extension,
	indexability);
	}

	dispatchRecordInterceptor(record) => JS('', '#.i', record);
	dispatchRecordProto(record) => JS('', '#.p', record);
	dispatchRecordExtension(record) => JS('', '#.e', record);
	dispatchRecordIndexability(record) => JS('bool\|Null', '#.x', record);

	/**
	* Returns the interceptor for a native class instance. Used by
	* [getInterceptor].
	*/
	getNativeInterceptor(object) {
	var record = getDispatchProperty(object);

	if (record == null) {
	if (initNativeDispatchFlag == null) {
	initNativeDispatch();
	record = getDispatchProperty(object);
	}
	}

	if (record != null) {
	var proto = dispatchRecordProto(record);
	if (false == proto) return dispatchRecordInterceptor(record);
	if (true == proto) return object;
	var objectProto = JS('', 'Object.getPrototypeOf(#)', object);
	if (JS('bool', '# === #', proto, objectProto)) {
	return dispatchRecordInterceptor(record);
	}

	var extension = dispatchRecordExtension(record);
	if (JS('bool', '# === #', extension, objectProto)) {
	// TODO(sra): The discriminator returns a tag. The tag is an uncached or
	// instance-cached tag, defaulting to instance-cached if caching
	// unspecified.
	var discriminatedTag = JS('', '(#)(#, #)', proto, object, record);
	throw new UnimplementedError('Return interceptor for $discriminatedTag');
	}
	}

	// Check for cached UnknownJavaScriptObject. This avoids doing the slow
	// dispatch-record based lookup for repeated js-interop classes.
	var constructor = JS('', '#.constructor', object);
	var interceptor = lookupInterceptorByConstructor(constructor);
	if (interceptor != null) return interceptor;

	// This takes care of dispatch-record based caching, but not constructor based
	// caching of [UnknownJavaScriptObject]s.
	interceptor = lookupAndCacheInterceptor(object);
	if (interceptor != null) return interceptor;

	// JavaScript Objects created via object literals and `Object.create(null)`
	// are 'plain' Objects. This test could be simplified and the dispatch path
	// be faster if Object.prototype was pre-patched with a non-leaf dispatch
	// record.
	if (JS('bool', 'typeof # == "function"', object)) {
	interceptor = JS_INTERCEPTOR_CONSTANT(JavaScriptFunction);
	// TODO(sra): Investigate caching on `Function`. It might be impossible if
	// some HTML embedded objects on some browsers are (still) JS functions.
	return interceptor;
	}
	var proto = JS('', 'Object.getPrototypeOf(#)', object);
	if (JS('bool', '# == null', proto)) {
	// Nowhere to cache output.
	return JS_INTERCEPTOR_CONSTANT(PlainJavaScriptObject);
	}
	interceptor = JS_INTERCEPTOR_CONSTANT(UnknownJavaScriptObject);
	if (JS('bool', '# === Object.prototype', proto)) {
	interceptor = JS_INTERCEPTOR_CONSTANT(PlainJavaScriptObject);
	// TODO(sra): Investigate caching on 'Object'. It might be impossible if
	// some native class is plain Object (e.g. like Firefox's ImageData).
	return interceptor;
	}
	if (JS('bool', 'typeof # == "function"', constructor)) {
	cacheInterceptorOnConstructor(constructor, interceptor);
	return interceptor;
	}
	return JS_INTERCEPTOR_CONSTANT(UnknownJavaScriptObject);
	}

	// A JS String or Symbol.
	final JS_INTEROP_INTERCEPTOR_TAG = getIsolateAffinityTag(r'_$dart_js');

	lookupInterceptorByConstructor(constructor) {
	return constructor == null
	? null
	: JS('', '#[#]', constructor, JS_INTEROP_INTERCEPTOR_TAG);
	}

	void cacheInterceptorOnConstructor(constructor, interceptor) {
	defineProperty(constructor, JS_INTEROP_INTERCEPTOR_TAG, interceptor);
	}

	var constructorToInterceptor =
	JS('', 'typeof(self.WeakMap) == "undefined" ? new Map() : new WeakMap()');

	XlookupInterceptorByConstructor(constructor) {
	return JS('', '#.get(#)', constructorToInterceptor, constructor);
	}

	void XcacheInterceptorOnConstructor(constructor, interceptor) {
	JS('', '#.set(#, #)', constructorToInterceptor, constructor, interceptor);
	}

	/**
	* Data structure used to map a [Type] to the [Interceptor] and constructors for
	* that type. It is JavaScript array of 3N entries of adjacent slots containing
	* a [Type], followed by an [Interceptor] class for the type, followed by a
	* JavaScript object map for the constructors.
	*
	* The value of this variable is set by the compiler and contains only types
	* that are user extensions of native classes where the type occurs as a
	* constant in the program.
	*
	* The compiler, in CustomElementsAnalysis, assumes that [typeToInterceptorMap]
	* is accessed only by code that also calls [findIndexForWebComponentType]. If
	* this assumption is invalidated, the compiler will have to be updated.
	*/
	get typeToInterceptorMap {
	return JS_EMBEDDED_GLOBAL('', TYPE_TO_INTERCEPTOR_MAP);
	}

	int findIndexForNativeSubclassType(Type type) {
	if (JS('bool', '# == null', typeToInterceptorMap)) return null;
	List map = JS('JSFixedArray', '#', typeToInterceptorMap);
	for (int i = 0; i + 1 < map.length; i += 3) {
	if (type == map[i]) {
	return i;
	}
	}
	return null;
	}

	findInterceptorConstructorForType(Type type) {
	var index = findIndexForNativeSubclassType(type);
	if (index == null) return null;
	List map = JS('JSFixedArray', '#', typeToInterceptorMap);
	return map[index + 1];
	}

	/**
	* Returns a JavaScript function that runs the constructor on its argument, or
	* `null` if there is no such constructor.
	*
	* The returned function takes one argument, the web component object.
	*/
	findConstructorForNativeSubclassType(Type type, String name) {
	var index = findIndexForNativeSubclassType(type);
	if (index == null) return null;
	List map = JS('JSFixedArray', '#', typeToInterceptorMap);
	var constructorMap = map[index + 2];
	var constructorFn = JS('', '#[#]', constructorMap, name);
	return constructorFn;
	}

	findInterceptorForType(Type type) {
	var constructor = findInterceptorConstructorForType(type);
	if (constructor == null) return null;
	return JS('', '#.prototype', constructor);
	}

	/**
	* The base interceptor class.
	*
	* The code `r.foo(a)` is compiled to `getInterceptor(r).foo$1(r, a)`. The
	* value returned by [getInterceptor] holds the methods separately from the
	* state of the instance. The compiler converts the methods on an interceptor
	* to take the Dart `this` argument as an explicit `receiver` argument. The
	* JavaScript `this` parameter is bound to the interceptor.
	*
	* In order to have uniform call sites, if a method is defined on an
	* interceptor, methods of that name on plain unintercepted classes also use the
	* interceptor calling convention. The plain classes are _self-interceptors_,
	* and for them, `getInterceptor(r)` returns `r`. Methods on plain
	* unintercepted classes have a redundant `receiver` argument and, to enable
	* some optimizations, must ignore `receiver` in favour of `this`.
	*
	* In the case of mixins, a method may be placed on both an intercepted class
	* and an unintercepted class. In this case, the method must use the `receiver`
	* parameter.
	*
	*
	* There are various optimizations of the general call pattern.
	*
	* When the interceptor can be statically determined, it can be used directly:
	*
	* CONSTANT_INTERCEPTOR.foo$1(r, a)
	*
	* If there are only a few classes, [getInterceptor] can be specialized with a
	* more efficient dispatch:
	*
	* getInterceptor$specialized(r).foo$1(r, a)
	*
	* If it can be determined that the receiver is an unintercepted class, it can
	* be called directly:
	*
	* r.foo$1(r, a)
	*
	* If, further, it is known that the call site cannot call a foo that is
	* mixed-in to a native class, then it is known that the explicit receiver is
	* ignored, and space-saving dummy value can be passed instead:
	*
	* r.foo$1(0, a)
	*
	* This class defines implementations of all methods on [Object] so no
	* interceptor inherits an implementation from [Object]. This enables the
	* implementations on Object to ignore the explicit receiver argument, which
	* allows dummy receiver optimization.
	*/
	abstract class Interceptor {
	const Interceptor();

	bool operator ==(other) => identical(this, other);

	int get hashCode => Primitives.objectHashCode(this);

	String toString() => Primitives.objectToHumanReadableString(this);

	// [Interceptor.noSuchMethod] is identical to [Object.noSuchMethod]. However,
	// each copy is compiled differently. The presence of the method on an
	// Interceptor class forces [noSuchMethod] to use interceptor calling
	// convention. In the [Interceptor] version, `this` is the explicit receiver
	// argument. In the [Object] version, as Object is not an intercepted class,
	// `this` is the JavaScript receiver, and the explicit receiver is ignored.
	// The noSuchMethod stubs for selectors that use the interceptor calling
	// convention do not know the calling convention and forward `this` and
	// `receiver` to one of these noSuchMethod implementations which selects the
	// correct Dart receiver.
	//
	// We don't allow [noSuchMethod] on intercepted classes (that would force all
	// calls to use interceptor calling convention). If we did allow it, the
	// interceptor context would select the correct `this`.
	dynamic noSuchMethod(Invocation invocation) {
	throw new NoSuchMethodError(this, invocation.memberName,
	invocation.positionalArguments, invocation.namedArguments);
	}

	Type get runtimeType => getRuntimeType(this);
	}

	/**
	* The interceptor class for [bool].
	*/
	class JSBool extends Interceptor implements bool {
	const JSBool();

	// Note: if you change this, also change the function [S].
	String toString() => JS('String', r'String(#)', this);

	bool operator &(bool other) => JS('bool', "# && #", checkBool(other), this);

	bool operator \|(bool other) => JS('bool', "# \|\| #", checkBool(other), this);

	bool operator ^(bool other) => !identical(this, checkBool(other));

	// The values here are SMIs, co-prime and differ about half of the bit
	// positions, including the low bit, so they are different mod 2^k.
	int get hashCode => this ? (2 * 3 * 23 * 3761) : (269 * 811);

	Type get runtimeType => bool;
	}

	/**
	* The interceptor class for [Null].
	*
	* This class defines implementations for all methods on [Object] since
	* the methods on Object assume the receiver is non-null. This means that
	* JSNull will always be in the interceptor set for methods defined on Object.
	*/
	class JSNull extends Interceptor implements Null {
	const JSNull();

	bool operator ==(other) => identical(null, other);

	// Note: if you change this, also change the function [S].
	String toString() => 'null';

	int get hashCode => 0;

	// The spec guarantees that `null` is the singleton instance of the `Null`
	// class. In the mirrors library we also have to patch the `type` getter to
	// special case `null`.
	Type get runtimeType => Null;

	dynamic noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
	}

	/**
	* The supertype for JSString and JSArray. Used by the backend as to
	* have a type mask that contains the objects that we can use the
	* native JS [] operator and length on.
	*/
	abstract class JSIndexable<E> {
	int get length;
	E operator [](int index);
	}

	/**
	* The supertype for JSMutableArray and
	* JavaScriptIndexingBehavior. Used by the backend to have a type mask
	* that contains the objects we can use the JS []= operator on.
	*/
	abstract class JSMutableIndexable<E> extends JSIndexable<E> {
	operator []=(int index, E value);
	}

	/**
	* The interface implemented by JavaScript objects. These are methods in
	* addition to the regular Dart Object methods like [Object.hashCode].
	*
	* This is the type that should be exported by a JavaScript interop library.
	*/
	abstract class JSObject {}

	/**
	* Interceptor base class for JavaScript objects not recognized as some more
	* specific native type.
	*/
	class JavaScriptObject extends Interceptor implements JSObject {
	const JavaScriptObject();

	// It would be impolite to stash a property on the object.
	int get hashCode => 0;

	Type get runtimeType => JSObject;

	/**
	* Returns the result of the JavaScript objects `toString` method.
	*/
	String toString() => JS('String', 'String(#)', this);
	}

	/**
	* Interceptor for plain JavaScript objects created as JavaScript object
	* literals or `new Object()`.
	*/
	class PlainJavaScriptObject extends JavaScriptObject {
	const PlainJavaScriptObject();
	}

	/**
	* Interceptor for unclassified JavaScript objects, typically objects with a
	* non-trivial prototype chain.
	*
	* This class also serves as a fallback for unknown JavaScript exceptions.
	*/
	class UnknownJavaScriptObject extends JavaScriptObject {
	const UnknownJavaScriptObject();
	}

	/**
	* Interceptor for JavaScript function objects and Dart functions that have
	* been converted to JavaScript functions.
	* These interceptor methods are not always used as the JavaScript function
	* object has also been mangled to support Dart function calling conventions.
	*/
	class JavaScriptFunction extends JavaScriptObject implements Function {
	const JavaScriptFunction();

	String toString() {
	var dartClosure = JS('', '#.#', this, DART_CLOSURE_PROPERTY_NAME);
	if (dartClosure == null) return super.toString();
	return 'JavaScript function for ${dartClosure.toString()}';
	}
	}