srujzs/web

Evolution of Dart Web, Browser, JS support

Lightweight browser API bindings built around JS interop.

What's this?

This package exposes browser APIs. It's generated from the Web IDL definitions and uses recent Dart language features for zero-overhead bindings.

This package is intended to replace dart:html and similar Dart SDK libraries. It will support access to browser APIs from Dart code compiled to either JavaScript or WebAssembly.

Usage

import 'package:web/web.dart';

void main() {
  final div = document.querySelector('div')!;
  div.text = 'Text set at ${DateTime.now()}';
}

Migrating to package:web

package:web is replacing dart:html and other web libraries as Dart's long-term web interop solution. To learn how to migrate from dart:html APIs to package:web, see our migration guide.

Generation conventions

The generator scripts use a number of conventions to consistently handle Web IDL definitions:

Interfaces

• Interfaces are emitted as extension types that wrap and implement JSObject.
• Interface inheritance is maintained using implements between extension types.
• Members of partial interfaces, partial mixins, and mixins are added to the interfaces that include them, and therefore do not have separate declarations.

Types

• Generic types include the generic in the case of JSArray and JSPromise.
• Enums are typedef'd to String.
• Callbacks and callback interfaces are typedef'd to JSFunction.
• In general, we prefer the Dart primitive over the JS type equivalent wherever possible. For example, APIs use String instead of JSString.
• If a type appears in a generic position and it was typedef'd to a Dart primitive type, it is replaced with the JS type equivalent to respect the type bound of JSAny?.
• Union types are computed by picking the least upper bound of the types in the JS type hierarchy, where every interface is equivalent to JSObject.
• Dictionary and typedef types are only emitted if they're used by another API.

Compatibility

• The generator uses the MDN compatibility data to determine what members, interfaces, and namespaces to emit. Currently, we only emit code that is standards track and is not experimental to reduce the number of breaking changes.

Generation and updating the package

Most of the APIs in this package are generated from public assets. See tool/README.md for information on the spec and IDL versions the package was generated from, and for the process for updating the package.