/**
* @license
* Copyright The Closure Library Authors.
* SPDX-License-Identifier: Apache-2.0
*/
/**
* @fileoverview Provides a function to schedule running a function as soon
* as possible after the current JS execution stops and yields to the event
* loop.
*/
goog.provide('goog.async.nextTick');
goog.require('goog.debug.entryPointRegistry');
goog.require('goog.dom');
goog.require('goog.dom.TagName');
goog.require('goog.functions');
goog.require('goog.labs.userAgent.browser');
goog.require('goog.labs.userAgent.engine');
/**
* Fires the provided callbacks as soon as possible after the current JS
* execution context. setTimeout(…, 0) takes at least 4ms when called from
* within another setTimeout(…, 0) for legacy reasons.
*
* This will not schedule the callback as a microtask (i.e. a task that can
* preempt user input or networking callbacks). It is meant to emulate what
* setTimeout(_, 0) would do if it were not throttled. If you desire microtask
* behavior, use {@see goog.Promise} instead.
*
* @param {function(this:SCOPE)} callback Callback function to fire as soon as
* possible.
* @param {SCOPE=} opt_context Object in whose scope to call the listener.
* @param {boolean=} opt_useSetImmediate Avoid the IE workaround that
* ensures correctness at the cost of speed. See comments for details.
* @template SCOPE
*/
goog.async.nextTick = function(callback, opt_context, opt_useSetImmediate) {
'use strict';
var cb = callback;
if (opt_context) {
cb = goog.bind(callback, opt_context);
}
cb = goog.async.nextTick.wrapCallback_(cb);
// Note we do allow callers to also request setImmediate if they are willing
// to accept the possible tradeoffs of incorrectness in exchange for speed.
// The IE fallback of readystate change is much slower. See useSetImmediate_
// for details.
if (typeof goog.global.setImmediate === 'function' &&
(opt_useSetImmediate || goog.async.nextTick.useSetImmediate_())) {
goog.global.setImmediate(cb);
return;
}
// Look for and cache the custom fallback version of setImmediate.
if (!goog.async.nextTick.setImmediate_) {
goog.async.nextTick.setImmediate_ =
goog.async.nextTick.getSetImmediateEmulator_();
}
goog.async.nextTick.setImmediate_(cb);
};
/**
* Returns whether should use setImmediate implementation currently on window.
*
* window.setImmediate was introduced and currently only supported by IE10+,
* but due to a bug in the implementation it is not guaranteed that
* setImmediate is faster than setTimeout nor that setImmediate N is before
* setImmediate N+1. That is why we do not use the native version if
* available. We do, however, call setImmediate if it is a non-native function
* because that indicates that it has been replaced by goog.testing.MockClock
* which we do want to support.
* See
* http://connect.microsoft.com/IE/feedback/details/801823/setimmediate-and-messagechannel-are-broken-in-ie10
*
* @return {boolean} Whether to use the implementation of setImmediate defined
* on Window.
* @private
* @suppress {missingProperties} For "Window.prototype.setImmediate"
*/
goog.async.nextTick.useSetImmediate_ = function() {
'use strict';
// Not a browser environment.
if (!goog.global.Window || !goog.global.Window.prototype) {
return true;
}
// MS Edge has window.setImmediate natively, but it's not on Window.prototype.
// Also, there's no clean way to detect if the goog.global.setImmediate has
// been replaced by mockClock as its replacement also shows up as "[native
// code]" when using toString. Therefore, just always use
// goog.global.setImmediate for Edge. It's unclear if it suffers the same
// issues as IE10/11, but based on
// https://dev.modern.ie/testdrive/demos/setimmediatesorting/
// it seems they've been working to ensure it's WAI.
if (goog.labs.userAgent.browser.isEdge() ||
goog.global.Window.prototype.setImmediate != goog.global.setImmediate) {
// Something redefined setImmediate in which case we decide to use it (This
// is so that we use the mockClock setImmediate).
return true;
}
return false;
};
/**
* Cache for the setImmediate implementation.
* @type {function(function())}
* @private
*/
goog.async.nextTick.setImmediate_;
/**
* Determines the best possible implementation to run a function as soon as
* the JS event loop is idle.
* @return {function(function())} The "setImmediate" implementation.
* @private
*/
goog.async.nextTick.getSetImmediateEmulator_ = function() {
'use strict';
// Create a private message channel and use it to postMessage empty messages
// to ourselves.
/** @type {!Function|undefined} */
var Channel = goog.global['MessageChannel'];
// If MessageChannel is not available and we are in a browser, implement
// an iframe based polyfill in browsers that have postMessage and
// document.addEventListener. The latter excludes IE8 because it has a
// synchronous postMessage implementation.
if (typeof Channel === 'undefined' && typeof window !== 'undefined' &&
window.postMessage && window.addEventListener &&
// Presto (The old pre-blink Opera engine) has problems with iframes
// and contentWindow.
!goog.labs.userAgent.engine.isPresto()) {
/** @constructor */
Channel = function() {
'use strict';
// Make an empty, invisible iframe.
var iframe = goog.dom.createElement(goog.dom.TagName.IFRAME);
iframe.style.display = 'none';
document.documentElement.appendChild(iframe);
var win = iframe.contentWindow;
var doc = win.document;
doc.open();
doc.close();
// Do not post anything sensitive over this channel, as the workaround for
// pages with file: origin could allow that information to be modified or
// intercepted.
var message = 'callImmediate' + Math.random();
// The same origin policy rejects attempts to postMessage from file: urls
// unless the origin is '*'.
var origin = win.location.protocol == 'file:' ?
'*' :
win.location.protocol + '//' + win.location.host;
var onmessage = goog.bind(function(e) {
'use strict';
// Validate origin and message to make sure that this message was
// intended for us. If the origin is set to '*' (see above) only the
// message needs to match since, for example, '*' != 'file://'. Allowing
// the wildcard is ok, as we are not concerned with security here.
if ((origin != '*' && e.origin != origin) || e.data != message) {
return;
}
this['port1'].onmessage();
}, this);
win.addEventListener('message', onmessage, false);
this['port1'] = {};
this['port2'] = {
postMessage: function() {
'use strict';
win.postMessage(message, origin);
}
};
};
}
if (typeof Channel !== 'undefined' && !goog.labs.userAgent.browser.isIE()) {
// Exclude all of IE due to
// http://codeforhire.com/2013/09/21/setimmediate-and-messagechannel-broken-on-internet-explorer-10/
// which allows starving postMessage with a busy setTimeout loop.
// This currently affects IE10 and IE11 which would otherwise be able
// to use the postMessage based fallbacks.
var channel = new Channel();
// Use a fifo linked list to call callbacks in the right order.
var head = {};
var tail = head;
channel['port1'].onmessage = function() {
'use strict';
if (head.next !== undefined) {
head = head.next;
var cb = head.cb;
head.cb = null;
cb();
}
};
return function(cb) {
'use strict';
tail.next = {cb: cb};
tail = tail.next;
channel['port2'].postMessage(0);
};
}
// Fall back to setTimeout with 0. In browsers this creates a delay of 5ms
// or more.
// NOTE(user): This fallback is used for IE.
return function(cb) {
'use strict';
goog.global.setTimeout(/** @type {function()} */ (cb), 0);
};
};
/**
* Helper function that is overrided to protect callbacks with entry point
* monitor if the application monitors entry points.
* @param {function()} callback Callback function to fire as soon as possible.
* @return {function()} The wrapped callback.
* @private
*/
goog.async.nextTick.wrapCallback_ = goog.functions.identity;
// Register the callback function as an entry point, so that it can be
// monitored for exception handling, etc. This has to be done in this file
// since it requires special code to handle all browsers.
goog.debug.entryPointRegistry.register(
/**
* @param {function(!Function): !Function} transformer The transforming
* function.
*/
function(transformer) {
'use strict';
goog.async.nextTick.wrapCallback_ = transformer;
});
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