dart web worker

main.dart

import 'communicator.dart';

void main() {
   final communicator = WorkerCommunicator('worker.dart.js')
      ..listen((event) {
        print('Data from worker: "$event"');
      });
  communicator.add('Ping'); 
}

pubspec.yaml

dev_dependencies:
  js: ^0.6.3

worker.dart

// Worker не надо подключать в index.html
// dart2js -o web/worker.dart.js lib/src/worker.dart

@JS()
library sample;

import 'dart:html';
import 'package:js/js.dart';

@JS('self')
external DedicatedWorkerGlobalScope get self;

void main() {
  self.onMessage.listen((e) {
    print('Message received from main script');
    var workerResult = 'Result: ${e.data}';
    print('Posting message back to main script');
    self.postMessage(workerResult, null);
  });
}

worker_communicator.dart

import 'dart:async';
import 'dart:html' as html;

abstract class Communicator<S, R> extends Stream<R> implements StreamSink<S> {}

class WorkerCommunicator<S extends Object, R extends Object> extends Communicator<S, R> {
  final html.Worker _worker;
  WorkerCommunicator(String scriptUrl) : _worker = html.Worker(scriptUrl) {
    if (!html.Worker.supported) {
      // ignore: avoid_escaping_inner_quotes
      throw UnsupportedError('Your browser doesn\'t support web workers.');
    }
  }

  @override
  void add(S event) => _worker.postMessage(event);

  @override
  void addError(Object error, [StackTrace? stackTrace]) => throw UnimplementedError();

  @override
  Future addStream(Stream<S> stream) => throw UnimplementedError();

  @override
  Future close() => throw UnimplementedError();

  @override
  Future get done => throw UnimplementedError();

  @override
  StreamSubscription<R> listen(
    void Function(R event)? onData, {
    Function? onError,
    void Function()? onDone,
    bool? cancelOnError,
  }) =>
      _worker.onMessage
          .where((e) => e.data is R)
          .map<R>((e) => e.data as R)
          .listen(
            onData,
            onError: onError,
            onDone: onDone,
            cancelOnError: cancelOnError,
          );
}