packages/integration_test/lib/src/_extension_web.dart

// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:async';
import 'dart:convert';
import 'dart:js_interop';
import 'dart:js_interop_unsafe';

@JS('window')
external JSObject get _window;

/// The web implementation of [registerWebServiceExtension].
///
/// Adds a hidden `window.$flutterDriver` JavaScript function that's called by
/// `FlutterWebDriver` to fulfill FlutterDriver commands.
///
/// See also:
///
///  * `_extension_io.dart`, which has the dart:io implementation
void registerWebServiceExtension(Future<Map<String, dynamic>> Function(Map<String, String>) callback) {
  // Define the result variable because packages/flutter_driver/lib/src/driver/web_driver.dart
  // checks for this value to become non-null when waiting for the result. If this value is
  // undefined at the time of the check, WebDriver throws an exception.
  _window.setProperty(r'$flutterDriverResult'.toJS, null);

  _window.setProperty(r'$flutterDriver'.toJS, (JSAny message) {
    (() async {
      try {
        final Map<String, dynamic> messageJson = jsonDecode((message as JSString).toDart) as Map<String, dynamic>;
        final Map<String, String> params = messageJson.cast<String, String>();
        final Map<String, dynamic> result = await callback(params);
        _window.setProperty(r'$flutterDriverResult'.toJS, json.encode(result).toJS);
      } catch (error, stackTrace) {
        // Encode the error in the same format the FlutterDriver extension uses.
        // See //packages/flutter_driver/lib/src/extension/extension.dart
        _window.setProperty(r'$flutterDriverResult'.toJS,
          json.encode(<String, dynamic>{
            'isError': true,
            'response': '$error\n$stackTrace',
          }).toJS
        );
      }
    })();
  }.toJS);
}