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
22goog.provide('goog.async.nextTick');
23goog.provide('goog.async.throwException');
24
25goog.require('goog.debug.entryPointRegistry');
26goog.require('goog.dom.TagName');
27goog.require('goog.functions');
28goog.require('goog.labs.userAgent.browser');
29goog.require('goog.labs.userAgent.engine');
30
31
32/**
33 * Throw an item without interrupting the current execution context. For
34 * example, if processing a group of items in a loop, sometimes it is useful
35 * to report an error while still allowing the rest of the batch to be
36 * processed.
37 * @param {*} exception
38 */
39goog.async.throwException = function(exception) {
40 // Each throw needs to be in its own context.
41 goog.global.setTimeout(function() { throw exception; }, 0);
42};
43
44
45/**
46 * Fires the provided callbacks as soon as possible after the current JS
47 * execution context. setTimeout(…, 0) takes at least 4ms when called from
48 * within another setTimeout(…, 0) for legacy reasons.
49 *
50 * This will not schedule the callback as a microtask (i.e. a task that can
51 * preempt user input or networking callbacks). It is meant to emulate what
52 * setTimeout(_, 0) would do if it were not throttled. If you desire microtask
53 * behavior, use {@see goog.Promise} instead.
54 *
55 * @param {function(this:SCOPE)} callback Callback function to fire as soon as
56 * possible.
57 * @param {SCOPE=} opt_context Object in whose scope to call the listener.
58 * @param {boolean=} opt_useSetImmediate Avoid the IE workaround that
59 * ensures correctness at the cost of speed. See comments for details.
60 * @template SCOPE
61 */
62goog.async.nextTick = function(callback, opt_context, opt_useSetImmediate) {
63 var cb = callback;
64 if (opt_context) {
65 cb = goog.bind(callback, opt_context);
66 }
67 cb = goog.async.nextTick.wrapCallback_(cb);
68 // window.setImmediate was introduced and currently only supported by IE10+,
69 // but due to a bug in the implementation it is not guaranteed that
70 // setImmediate is faster than setTimeout nor that setImmediate N is before
71 // setImmediate N+1. That is why we do not use the native version if
72 // available. We do, however, call setImmediate if it is a normal function
73 // because that indicates that it has been replaced by goog.testing.MockClock
74 // which we do want to support.
75 // See
76 // http://connect.microsoft.com/IE/feedback/details/801823/setimmediate-and-messagechannel-are-broken-in-ie10
77 //
78 // Note we do allow callers to also request setImmediate if they are willing
79 // to accept the possible tradeoffs of incorrectness in exchange for speed.
80 // The IE fallback of readystate change is much slower.
81 if (goog.isFunction(goog.global.setImmediate) &&
82 // Opt in.
83 (opt_useSetImmediate ||
84 // or it isn't a browser or the environment is weird
85 !goog.global.Window || !goog.global.Window.prototype ||
86 // or something redefined setImmediate in which case we (YOLO) decide
87 // to use it (This is so that we use the mockClock setImmediate. sigh).
88 goog.global.Window.prototype.setImmediate != goog.global.setImmediate)) {
89 goog.global.setImmediate(cb);
90 return;
91 }
92
93 // Look for and cache the custom fallback version of setImmediate.
94 if (!goog.async.nextTick.setImmediate_) {
95 goog.async.nextTick.setImmediate_ =
96 goog.async.nextTick.getSetImmediateEmulator_();
97 }
98 goog.async.nextTick.setImmediate_(cb);
99};
100
101
102/**
103 * Cache for the setImmediate implementation.
104 * @type {function(function())}
105 * @private
106 */
107goog.async.nextTick.setImmediate_;
108
109
110/**
111 * Determines the best possible implementation to run a function as soon as
112 * the JS event loop is idle.
113 * @return {function(function())} The "setImmediate" implementation.
114 * @private
115 */
116goog.async.nextTick.getSetImmediateEmulator_ = function() {
117 // Create a private message channel and use it to postMessage empty messages
118 // to ourselves.
119 var Channel = goog.global['MessageChannel'];
120 // If MessageChannel is not available and we are in a browser, implement
121 // an iframe based polyfill in browsers that have postMessage and
122 // document.addEventListener. The latter excludes IE8 because it has a
123 // synchronous postMessage implementation.
124 if (typeof Channel === 'undefined' && typeof window !== 'undefined' &&
125 window.postMessage && window.addEventListener &&
126 // Presto (The old pre-blink Opera engine) has problems with iframes
127 // and contentWindow.
128 !goog.labs.userAgent.engine.isPresto()) {
129 /** @constructor */
130 Channel = function() {
131 // Make an empty, invisible iframe.
132 var iframe = document.createElement(goog.dom.TagName.IFRAME);
133 iframe.style.display = 'none';
134 iframe.src = '';
135 document.documentElement.appendChild(iframe);
136 var win = iframe.contentWindow;
137 var doc = win.document;
138 doc.open();
139 doc.write('');
140 doc.close();
141 // Do not post anything sensitive over this channel, as the workaround for
142 // pages with file: origin could allow that information to be modified or
143 // intercepted.
144 var message = 'callImmediate' + Math.random();
145 // The same origin policy rejects attempts to postMessage from file: urls
146 // unless the origin is '*'.
147 // TODO(b/16335441): Use '*' origin for data: and other similar protocols.
148 var origin = win.location.protocol == 'file:' ?
149 '*' : win.location.protocol + '//' + win.location.host;
150 var onmessage = goog.bind(function(e) {
151 // Validate origin and message to make sure that this message was
152 // intended for us. If the origin is set to '*' (see above) only the
153 // message needs to match since, for example, '*' != 'file://'. Allowing
154 // the wildcard is ok, as we are not concerned with security here.
155 if ((origin != '*' && e.origin != origin) || e.data != message) {
156 return;
157 }
158 this['port1'].onmessage();
159 }, this);
160 win.addEventListener('message', onmessage, false);
161 this['port1'] = {};
162 this['port2'] = {
163 postMessage: function() {
164 win.postMessage(message, origin);
165 }
166 };
167 };
168 }
169 if (typeof Channel !== 'undefined' &&
170 (!goog.labs.userAgent.browser.isIE())) {
171 // Exclude all of IE due to
172 // http://codeforhire.com/2013/09/21/setimmediate-and-messagechannel-broken-on-internet-explorer-10/
173 // which allows starving postMessage with a busy setTimeout loop.
174 // This currently affects IE10 and IE11 which would otherwise be able
175 // to use the postMessage based fallbacks.
176 var channel = new Channel();
177 // Use a fifo linked list to call callbacks in the right order.
178 var head = {};
179 var tail = head;
180 channel['port1'].onmessage = function() {
181 if (goog.isDef(head.next)) {
182 head = head.next;
183 var cb = head.cb;
184 head.cb = null;
185 cb();
186 }
187 };
188 return function(cb) {
189 tail.next = {
190 cb: cb
191 };
192 tail = tail.next;
193 channel['port2'].postMessage(0);
194 };
195 }
196 // Implementation for IE6+: Script elements fire an asynchronous
197 // onreadystatechange event when inserted into the DOM.
198 if (typeof document !== 'undefined' && 'onreadystatechange' in
199 document.createElement(goog.dom.TagName.SCRIPT)) {
200 return function(cb) {
201 var script = document.createElement(goog.dom.TagName.SCRIPT);
202 script.onreadystatechange = function() {
203 // Clean up and call the callback.
204 script.onreadystatechange = null;
205 script.parentNode.removeChild(script);
206 script = null;
207 cb();
208 cb = null;
209 };
210 document.documentElement.appendChild(script);
211 };
212 }
213 // Fall back to setTimeout with 0. In browsers this creates a delay of 5ms
214 // or more.
215 return function(cb) {
216 goog.global.setTimeout(cb, 0);
217 };
218};
219
220
221/**
222 * Helper function that is overrided to protect callbacks with entry point
223 * monitor if the application monitors entry points.
224 * @param {function()} callback Callback function to fire as soon as possible.
225 * @return {function()} The wrapped callback.
226 * @private
227 */
228goog.async.nextTick.wrapCallback_ = goog.functions.identity;
229
230
231// Register the callback function as an entry point, so that it can be
232// monitored for exception handling, etc. This has to be done in this file
233// since it requires special code to handle all browsers.
234goog.debug.entryPointRegistry.register(
235 /**
236 * @param {function(!Function): !Function} transformer The transforming
237 * function.
238 */
239 function(transformer) {
240 goog.async.nextTick.wrapCallback_ = transformer;
241 });