Imports and exports

NOTE: This is for internal usage only and not intended for end-users (yet). See tracking issue for eventually exposing this at github.com/dart-lang/sdk/issues/55856

To import a function, declare it as a global, external function and mark it with a wasm:import pragma indicating the imported name (which must be two identifiers separated by a dot):

@pragma("wasm:import", "foo.bar")
external void fooBar(Object object);

which will call foo.bar on the host side:

var foo = {
    bar: function(object) { /* implementation here */ }
};

To export a function, mark it with a wasm:export pragma:

@pragma("wasm:export")
void foo(double x) { /* implementation here */  }

@pragma("wasm:export", "baz")
void bar(double x) { /* implementation here */  }

With the Wasm module instance in inst, these can be called as:

inst.exports.foo(1);
inst.exports.baz(2);

Types to use for interop

In the signatures of imported and exported functions, use the following types:

• For numbers, use double.
• For JS objects, use a JS interop type, e.g. JSAny, which translates to the Wasm externref type. These can be passed around and stored as opaque values on the Dart side.
• For Dart objects, use the corresponding Dart type. This will be emitted as anyref and automatically converted to and from externref at the boundary