A stream wrapping JavaScript's window.onmessage that is safe to import even on platforms other than web.

Purpose

In web apps, you can listen to events from other frames like this:

import 'dart:html' as html;

void main() {
  html.window.onMessage.listen((html.MessageEvent event) {
    // Handle.
  });
  // ...
}

However, dart:html is not available on platforms other than web. If you use it, your app cannot be built there.

The Dart team recommends conditional import of files that use dart:html which gets your app complex. And even then you must silence a linter warning of importing dart:html in a non-web-only package.

This package provides a wrapper for that stream of messages that can be used on all platforms. On platforms other than web, the stream would just produce no events.

Usage

import 'package:onmessage/onmessage.dart';

void main() {
  OnMessage.instance.stream.listen((MessageEvent event) {
    // Handle.
  });
  // ...
}

MessageEvent class from this package is an independent class with fields copied from the original html.MessageEvent. It is provided so that you can have an API independent from web.