# lib/goog/async/nexttick.js

1 | // Copyright 2013 The Closure Library Authors. All Rights Reserved.
2 | //
3 | // Licensed under the Apache License, Version 2.0 (the "License");
4 | // you may not use this file except in compliance with the License.
5 | // You may obtain a copy of the License at
6 | //
7 | // http://www.apache.org/licenses/LICENSE-2.0
8 | //
9 | // Unless required by applicable law or agreed to in writing, software
10 | // distributed under the License is distributed on an "AS-IS" BASIS,
11 | // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 | // See the License for the specific language governing permissions and
13 | // limitations under the License.
14 |
15 | /**
16 | * @fileoverview Provides a function to schedule running a function as soon
17 | * as possible after the current JS execution stops and yields to the event
18 | * loop.
19 | *
20 | */
21 |
22 | goog.provide('goog.async.nextTick');
23 | goog.provide('goog.async.throwException');
24 |
25 | goog.require('goog.debug.entryPointRegistry');
26 | goog.require('goog.functions');
27 | goog.require('goog.labs.userAgent.browser');
28 |
29 |
30 | /**
31 | * Throw an item without interrupting the current execution context. For
32 | * example, if processing a group of items in a loop, sometimes it is useful
33 | * to report an error while still allowing the rest of the batch to be
34 | * processed.
35 | * @param {*} exception
36 | */
37 | goog.async.throwException = function(exception) {
38 | // Each throw needs to be in its own context.
39 | goog.global.setTimeout(function() { throw exception; }, 0);
40 | };
41 |
42 |
43 | /**
44 | * Fires the provided callbacks as soon as possible after the current JS
45 | * execution context. setTimeout(…, 0) takes at least 4ms when called from
46 | * within another setTimeout(…, 0) for legacy reasons.
47 | *
48 | * This will not schedule the callback as a microtask (i.e. a task that can
49 | * preempt user input or networking callbacks). It is meant to emulate what
50 | * setTimeout(_, 0) would do if it were not throttled. If you desire microtask
51 | * behavior, use {@see goog.Promise} instead.
52 | *
53 | * @param {function(this:SCOPE)} callback Callback function to fire as soon as
54 | * possible.
55 | * @param {SCOPE=} opt_context Object in whose scope to call the listener.
56 | * @param {boolean=} opt_useSetImmediate Avoid the IE workaround that
57 | * ensures correctness at the cost of speed. See comments for details.
58 | * @template SCOPE
59 | */
60 | goog.async.nextTick = function(callback, opt_context, opt_useSetImmediate) {
61 | var cb = callback;
62 | if (opt_context) {
63 | cb = goog.bind(callback, opt_context);
64 | }
65 | cb = goog.async.nextTick.wrapCallback_(cb);
66 | // window.setImmediate was introduced and currently only supported by IE10+,
67 | // but due to a bug in the implementation it is not guaranteed that
68 | // setImmediate is faster than setTimeout nor that setImmediate N is before
69 | // setImmediate N+1. That is why we do not use the native version if
70 | // available. We do, however, call setImmediate if it is a normal function
71 | // because that indicates that it has been replaced by goog.testing.MockClock
72 | // which we do want to support.
73 | // See
74 | // http://connect.microsoft.com/IE/feedback/details/801823/setimmediate-and-messagechannel-are-broken-in-ie10
75 | //
76 | // Note we do allow callers to also request setImmediate if they are willing
77 | // to accept the possible tradeoffs of incorrectness in exchange for speed.
78 | // The IE fallback of readystate change is much slower.
79 | if (goog.isFunction(goog.global.setImmediate) &&
80 | (opt_useSetImmediate || !goog.global.Window ||
81 | goog.global.Window.prototype.setImmediate != goog.global.setImmediate)) {
82 | goog.global.setImmediate(cb);
83 | return;
84 | }
85 |
86 | // Look for and cache the custom fallback version of setImmediate.
87 | if (!goog.async.nextTick.setImmediate_) {
88 | goog.async.nextTick.setImmediate_ =
89 | goog.async.nextTick.getSetImmediateEmulator_();
90 | }
91 | goog.async.nextTick.setImmediate_(cb);
92 | };
93 |
94 |
95 | /**
96 | * Cache for the setImmediate implementation.
97 | * @type {function(function())}
98 | * @private
99 | */
100 | goog.async.nextTick.setImmediate_;
101 |
102 |
103 | /**
104 | * Determines the best possible implementation to run a function as soon as
105 | * the JS event loop is idle.
106 | * @return {function(function())} The "setImmediate" implementation.
107 | * @private
108 | */
109 | goog.async.nextTick.getSetImmediateEmulator_ = function() {
110 | // Create a private message channel and use it to postMessage empty messages
111 | // to ourselves.
112 | var Channel = goog.global['MessageChannel'];
113 | // If MessageChannel is not available and we are in a browser, implement
114 | // an iframe based polyfill in browsers that have postMessage and
115 | // document.addEventListener. The latter excludes IE8 because it has a
116 | // synchronous postMessage implementation.
117 | if (typeof Channel === 'undefined' && typeof window !== 'undefined' &&
118 | window.postMessage && window.addEventListener) {
119 | /** @constructor */
120 | Channel = function() {
121 | // Make an empty, invisible iframe.
122 | var iframe = document.createElement('iframe');
123 | iframe.style.display = 'none';
124 | iframe.src = '';
125 | document.documentElement.appendChild(iframe);
126 | var win = iframe.contentWindow;
127 | var doc = win.document;
128 | doc.open();
129 | doc.write('');
130 | doc.close();
131 | // Do not post anything sensitive over this channel, as the workaround for
132 | // pages with file: origin could allow that information to be modified or
133 | // intercepted.
134 | var message = 'callImmediate' + Math.random();
135 | // The same origin policy rejects attempts to postMessage from file: urls
136 | // unless the origin is '*'.
137 | // TODO(b/16335441): Use '*' origin for data: and other similar protocols.
138 | var origin = win.location.protocol == 'file:' ?
139 | '*' : win.location.protocol + '//' + win.location.host;
140 | var onmessage = goog.bind(function(e) {
141 | // Validate origin and message to make sure that this message was
142 | // intended for us. If the origin is set to '*' (see above) only the
143 | // message needs to match since, for example, '*' != 'file://'. Allowing
144 | // the wildcard is ok, as we are not concerned with security here.
145 | if ((origin != '*' && e.origin != origin) || e.data != message) {
146 | return;
147 | }
148 | this['port1'].onmessage();
149 | }, this);
150 | win.addEventListener('message', onmessage, false);
151 | this['port1'] = {};
152 | this['port2'] = {
153 | postMessage: function() {
154 | win.postMessage(message, origin);
155 | }
156 | };
157 | };
158 | }
159 | if (typeof Channel !== 'undefined' &&
160 | (!goog.labs.userAgent.browser.isIE())) {
161 | // Exclude all of IE due to
162 | // http://codeforhire.com/2013/09/21/setimmediate-and-messagechannel-broken-on-internet-explorer-10/
163 | // which allows starving postMessage with a busy setTimeout loop.
164 | // This currently affects IE10 and IE11 which would otherwise be able
165 | // to use the postMessage based fallbacks.
166 | var channel = new Channel();
167 | // Use a fifo linked list to call callbacks in the right order.
168 | var head = {};
169 | var tail = head;
170 | channel['port1'].onmessage = function() {
171 | if (goog.isDef(head.next)) {
172 | head = head.next;
173 | var cb = head.cb;
174 | head.cb = null;
175 | cb();
176 | }
177 | };
178 | return function(cb) {
179 | tail.next = {
180 | cb: cb
181 | };
182 | tail = tail.next;
183 | channel['port2'].postMessage(0);
184 | };
185 | }
186 | // Implementation for IE6+: Script elements fire an asynchronous
187 | // onreadystatechange event when inserted into the DOM.
188 | if (typeof document !== 'undefined' && 'onreadystatechange' in
189 | document.createElement('script')) {
190 | return function(cb) {
191 | var script = document.createElement('script');
192 | script.onreadystatechange = function() {
193 | // Clean up and call the callback.
194 | script.onreadystatechange = null;
195 | script.parentNode.removeChild(script);
196 | script = null;
197 | cb();
198 | cb = null;
199 | };
200 | document.documentElement.appendChild(script);
201 | };
202 | }
203 | // Fall back to setTimeout with 0. In browsers this creates a delay of 5ms
204 | // or more.
205 | return function(cb) {
206 | goog.global.setTimeout(cb, 0);
207 | };
208 | };
209 |
210 |
211 | /**
212 | * Helper function that is overrided to protect callbacks with entry point
213 | * monitor if the application monitors entry points.
214 | * @param {function()} callback Callback function to fire as soon as possible.
215 | * @return {function()} The wrapped callback.
216 | * @private
217 | */
218 | goog.async.nextTick.wrapCallback_ = goog.functions.identity;
219 |
220 |
221 | // Register the callback function as an entry point, so that it can be
222 | // monitored for exception handling, etc. This has to be done in this file
223 | // since it requires special code to handle all browsers.
224 | goog.debug.entryPointRegistry.register(
225 | /**
226 | * @param {function(!Function): !Function} transformer The transforming
227 | * function.
228 | */
229 | function(transformer) {
230 | goog.async.nextTick.wrapCallback_ = transformer;
231 | });