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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
"use strict";
var EXPORTED_SYMBOLS = ["PromiseUtils"];
var PromiseUtils = {
* Creates a new pending Promise and provide methods to resolve and reject this Promise.
* @return {Deferred} an object consisting of a pending Promise "promise"
* and methods "resolve" and "reject" to change its state.
defer() {
return new Deferred();
* Requests idle dispatch to the main thread for the given callback,
* and returns a promise which resolves to the callback's return value
* when it has been executed.
* @param {function} callback
* @param {integer} [timeout]
* An optional timeout, after which the callback will be
* executed immediately if idle dispatch has not yet occurred.
* @returns {Promise}
idleDispatch(callback, timeout = 0) {
return new Promise((resolve, reject) => { => {
try {
} catch (e) {
}, timeout);
* The definition of Deferred object which is returned by PromiseUtils.defer(),
* It contains a Promise and methods to resolve/reject it.
function Deferred() {
/* A method to resolve the associated Promise with the value passed.
* If the promise is already settled it does nothing.
* @param {anything} value : This value is used to resolve the promise
* If the value is a Promise then the associated promise assumes the state
* of Promise passed as value.
this.resolve = null;
/* A method to reject the assocaited Promise with the value passed.
* If the promise is already settled it does nothing.
* @param {anything} reason: The reason for the rejection of the Promise.
* Generally its an Error object. If however a Promise is passed, then the Promise
* itself will be the reason for rejection no matter the state of the Promise.
this.reject = null;
/* A newly created Pomise object.
* Initially in pending state.
this.promise = new Promise((resolve, reject) => {
this.resolve = resolve;
this.reject = reject;