sdk/lib/_internal/lib/async_patch.dart

// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

// Patch file for the dart:async library.

import 'dart:_isolate_helper' show IsolateNatives, TimerImpl;
import 'dart:_foreign_helper' show JS, DART_CLOSURE_TO_JS;

patch class Timer {
  patch factory Timer(Duration duration, void callback()) {
    int milliseconds = duration.inMilliseconds;
    if (milliseconds < 0) milliseconds = 0;
    return new TimerImpl(milliseconds, callback);
  }

  patch factory Timer.periodic(Duration duration, void callback(Timer timer)) {
    int milliseconds = duration.inMilliseconds;
    if (milliseconds < 0) milliseconds = 0;
    return new TimerImpl.periodic(milliseconds, callback);
  }
}

patch class _AsyncRun {
  patch static void _enqueueImmediate(void callback()) {
    // TODO(9002): don't use the Timer to enqueue the immediate callback.
    Timer.run(callback);
  }
}

patch class DeferredLibrary {
  patch Future<bool> load() {
    return _load(libraryName, uri);
  }
}

// TODO(ahe): This should not only apply to this isolate.
final _loadedLibraries = <String, Completer<bool>>{};

Future<bool> _load(String libraryName, String uri) {
  // TODO(ahe): Validate libraryName.  Kasper points out that you want
  // to be able to experiment with the effect of toggling @DeferLoad,
  // so perhaps we should silently ignore "bad" library names.
  Completer completer = new Completer<bool>();
  Future<bool> future = _loadedLibraries[libraryName];
  if (future != null) {
    future.then((_) { completer.complete(false); });
    return completer.future;
  }
  _loadedLibraries[libraryName] = completer.future;

  if (uri == null) {
    uri = IsolateNatives.thisScript;
    int index = uri.lastIndexOf('/');
    uri = '${uri.substring(0, index + 1)}part.js';
  }

  if (_hasDocument) {
    // Inject a script tag.
    var script = JS('', 'document.createElement("script")');
    JS('', '#.type = "text/javascript"', script);
    JS('', '#.async = "async"', script);
    JS('', '#.src = #', script, uri);
    var onLoad = JS('', '#.bind(null, #)',
                    DART_CLOSURE_TO_JS(_onDeferredLibraryLoad), completer);
    JS('', '#.addEventListener("load", #, false)', script, onLoad);
    JS('', 'document.body.appendChild(#)', script);
  } else if (JS('String', 'typeof load') == 'function') {
    Timer.run(() {
      JS('void', 'load(#)', uri);
      completer.complete(true);
    });
  } else {
    throw new UnsupportedError('load not supported');
  }
  return completer.future;
}

/// Used to implement deferred loading. Used as callback on "load"
/// event above in [load].
_onDeferredLibraryLoad(Completer<bool> completer, event) {
  completer.complete(true);
}

bool get _hasDocument => JS('String', 'typeof document') == 'object';