feat(scheduling): Support Promise.then() fallbacks to enqueue a microtask

Author: vicb

dist/zone-microtask.js

@@ -1111,21 +1111,9 @@ module.exports = {
 
 }).call(this,{},typeof global !== "undefined" ? global : typeof self !== "undefined" ? self : typeof window !== "undefined" ? window : {})
 },{}],4:[function(require,module,exports){
+(function (global){
 'use strict';
 
-// TODO(vicb) asap implementation should work if Promise is not available
-// es6-promise has fallbacks
-
-if (typeof Promise === "undefined" || Promise.toString().indexOf("[native code]") === -1) {
-  throw new Error('Promise is not available natively !')
-}
-
-var resolvedPromise = Promise.resolve(void 0);
-
-function asap(fn) {
-  resolvedPromise.then(fn);
-}
-
 function scheduleMicrotask(fn) {
   asap(this.bind(fn));
 }
@@ -1139,6 +1127,96 @@ module.exports = {
   addMicrotaskSupport: addMicrotaskSupport
 };
 
+// TODO(vicb): There are plan to be able to use asap() from es6-promise
+// see https://github.com/jakearchibald/es6-promise/pull/113
+// for now adapt code from asap.js in es6-promise
+// Note: the node support has been dropped here
+
+// TODO(vicb): Create a benchmark for the different methods & the usage of the queue
+// see https://github.com/angular/zone.js/issues/97
+
+var hasNativePromise = false;
+var len = 0;
+
+if (typeof Promise ==! "undefined" && Promise.toString().indexOf("[native code]") !== -1) {
+  hasNativePromise = true;
+}
+
+function asap(callback) {
+  queue[len] = callback;
+  len += 1;
+  if (len === 1) {
+    scheduleFlush();
+  }
+}
+
+var browserWindow = (typeof global.window !== 'undefined') ? global.window : undefined;
+var browserGlobal = browserWindow || {};
+var BrowserMutationObserver = browserGlobal.MutationObserver || browserGlobal.WebKitMutationObserver;
+
+// test for web worker but not in IE10
+var isWorker = typeof Uint8ClampedArray !== 'undefined' &&
+  typeof importScripts !== 'undefined' &&
+  typeof MessageChannel !== 'undefined';
+
+function useMutationObserver() {
+  var iterations = 0;
+  var observer = new BrowserMutationObserver(flush);
+  var node = document.createTextNode('');
+  observer.observe(node, { characterData: true });
+
+  return function() {
+    node.data = (iterations = ++iterations % 2);
+  };
+}
+
+// web worker
+function useMessageChannel() {
+  var channel = new MessageChannel();
+  channel.port1.onmessage = flush;
+  return function () {
+    channel.port2.postMessage(0);
+  };
+}
+
+function useSetTimeout() {
+  return function() {
+    setTimeout(flush, 1);
+  };
+}
+
+function usePromise() {
+  var resolvedPromise = Promise.resolve(void 0);
+  return function() {
+    resolvedPromise.then(flush);
+  }
+}
+
+var queue = new Array(1000);
+
+function flush() {
+  for (var i = 0; i < len; i++) {
+    var callback = queue[i];
+    callback();
+    queue[i] = undefined;
+  }
+
+  len = 0;
+}
+
+var scheduleFlush;
+// Decide what async method to use to triggering processing of queued callbacks:
+if (hasNativePromise) {
+  scheduleFlush = usePromise();
+} else if (BrowserMutationObserver) {
+  scheduleFlush = useMutationObserver();
+} else if (isWorker) {
+  scheduleFlush = useMessageChannel();
+} else {
+  scheduleFlush = useSetTimeout();
+}
+
+}).call(this,typeof global !== "undefined" ? global : typeof self !== "undefined" ? self : typeof window !== "undefined" ? window : {})
 },{}],5:[function(require,module,exports){
 (function (global){
 'use strict';