1159 lines
28 KiB
JavaScript
1159 lines
28 KiB
JavaScript
/*!
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* @overview es6-promise - a tiny implementation of Promises/A+.
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* @copyright Copyright (c) 2014 Yehuda Katz, Tom Dale, Stefan Penner and contributors (Conversion to ES6 API by Jake Archibald)
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* @license Licensed under MIT license
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* See https://raw.githubusercontent.com/stefanpenner/es6-promise/master/LICENSE
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* @version 4.0.5
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*/
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(function (global, factory) {
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typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
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typeof define === 'function' && define.amd ? define(factory) :
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(global.ES6Promise = factory());
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}(this, (function () { 'use strict';
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function objectOrFunction(x) {
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return typeof x === 'function' || typeof x === 'object' && x !== null;
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}
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function isFunction(x) {
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return typeof x === 'function';
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}
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var _isArray = undefined;
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if (!Array.isArray) {
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_isArray = function (x) {
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return Object.prototype.toString.call(x) === '[object Array]';
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};
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} else {
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_isArray = Array.isArray;
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}
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var isArray = _isArray;
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var len = 0;
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var vertxNext = undefined;
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var customSchedulerFn = undefined;
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var asap = function asap(callback, arg) {
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queue[len] = callback;
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queue[len + 1] = arg;
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len += 2;
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if (len === 2) {
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// If len is 2, that means that we need to schedule an async flush.
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// If additional callbacks are queued before the queue is flushed, they
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// will be processed by this flush that we are scheduling.
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if (customSchedulerFn) {
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customSchedulerFn(flush);
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} else {
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scheduleFlush();
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}
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}
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};
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function setScheduler(scheduleFn) {
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customSchedulerFn = scheduleFn;
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}
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function setAsap(asapFn) {
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asap = asapFn;
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}
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var browserWindow = typeof window !== 'undefined' ? window : undefined;
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var browserGlobal = browserWindow || {};
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var BrowserMutationObserver = browserGlobal.MutationObserver || browserGlobal.WebKitMutationObserver;
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var isNode = typeof self === 'undefined' && typeof process !== 'undefined' && ({}).toString.call(process) === '[object process]';
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// test for web worker but not in IE10
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var isWorker = typeof Uint8ClampedArray !== 'undefined' && typeof importScripts !== 'undefined' && typeof MessageChannel !== 'undefined';
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// node
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function useNextTick() {
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// node version 0.10.x displays a deprecation warning when nextTick is used recursively
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// see https://github.com/cujojs/when/issues/410 for details
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return function () {
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return process.nextTick(flush);
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};
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}
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// vertx
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function useVertxTimer() {
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if (typeof vertxNext !== 'undefined') {
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return function () {
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vertxNext(flush);
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};
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}
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return useSetTimeout();
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}
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function useMutationObserver() {
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var iterations = 0;
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var observer = new BrowserMutationObserver(flush);
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var node = document.createTextNode('');
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observer.observe(node, { characterData: true });
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return function () {
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node.data = iterations = ++iterations % 2;
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};
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}
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// web worker
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function useMessageChannel() {
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var channel = new MessageChannel();
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channel.port1.onmessage = flush;
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return function () {
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return channel.port2.postMessage(0);
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};
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}
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function useSetTimeout() {
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// Store setTimeout reference so es6-promise will be unaffected by
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// other code modifying setTimeout (like sinon.useFakeTimers())
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var globalSetTimeout = setTimeout;
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return function () {
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return globalSetTimeout(flush, 1);
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};
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}
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var queue = new Array(1000);
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function flush() {
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for (var i = 0; i < len; i += 2) {
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var callback = queue[i];
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var arg = queue[i + 1];
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callback(arg);
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queue[i] = undefined;
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queue[i + 1] = undefined;
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}
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len = 0;
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}
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function attemptVertx() {
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try {
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var r = require;
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var vertx = r('vertx');
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vertxNext = vertx.runOnLoop || vertx.runOnContext;
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return useVertxTimer();
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} catch (e) {
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return useSetTimeout();
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}
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}
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var scheduleFlush = undefined;
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// Decide what async method to use to triggering processing of queued callbacks:
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if (isNode) {
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scheduleFlush = useNextTick();
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} else if (BrowserMutationObserver) {
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scheduleFlush = useMutationObserver();
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} else if (isWorker) {
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scheduleFlush = useMessageChannel();
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} else if (browserWindow === undefined && typeof require === 'function') {
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scheduleFlush = attemptVertx();
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} else {
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scheduleFlush = useSetTimeout();
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}
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function then(onFulfillment, onRejection) {
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var _arguments = arguments;
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var parent = this;
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var child = new this.constructor(noop);
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if (child[PROMISE_ID] === undefined) {
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makePromise(child);
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}
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var _state = parent._state;
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if (_state) {
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(function () {
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var callback = _arguments[_state - 1];
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asap(function () {
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return invokeCallback(_state, child, callback, parent._result);
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});
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})();
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} else {
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subscribe(parent, child, onFulfillment, onRejection);
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}
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return child;
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}
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/**
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`Promise.resolve` returns a promise that will become resolved with the
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passed `value`. It is shorthand for the following:
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```javascript
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let promise = new Promise(function(resolve, reject){
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resolve(1);
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});
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promise.then(function(value){
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// value === 1
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});
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```
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Instead of writing the above, your code now simply becomes the following:
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```javascript
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let promise = Promise.resolve(1);
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promise.then(function(value){
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// value === 1
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});
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```
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@method resolve
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@static
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@param {Any} value value that the returned promise will be resolved with
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Useful for tooling.
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@return {Promise} a promise that will become fulfilled with the given
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`value`
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*/
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function resolve(object) {
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/*jshint validthis:true */
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var Constructor = this;
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if (object && typeof object === 'object' && object.constructor === Constructor) {
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return object;
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}
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var promise = new Constructor(noop);
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_resolve(promise, object);
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return promise;
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}
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var PROMISE_ID = Math.random().toString(36).substring(16);
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function noop() {}
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var PENDING = void 0;
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var FULFILLED = 1;
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var REJECTED = 2;
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var GET_THEN_ERROR = new ErrorObject();
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function selfFulfillment() {
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return new TypeError("You cannot resolve a promise with itself");
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}
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function cannotReturnOwn() {
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return new TypeError('A promises callback cannot return that same promise.');
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}
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function getThen(promise) {
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try {
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return promise.then;
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} catch (error) {
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GET_THEN_ERROR.error = error;
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return GET_THEN_ERROR;
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}
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}
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function tryThen(then, value, fulfillmentHandler, rejectionHandler) {
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try {
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then.call(value, fulfillmentHandler, rejectionHandler);
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} catch (e) {
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return e;
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}
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}
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function handleForeignThenable(promise, thenable, then) {
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asap(function (promise) {
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var sealed = false;
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var error = tryThen(then, thenable, function (value) {
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if (sealed) {
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return;
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}
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sealed = true;
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if (thenable !== value) {
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_resolve(promise, value);
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} else {
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fulfill(promise, value);
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}
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}, function (reason) {
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if (sealed) {
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return;
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}
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sealed = true;
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_reject(promise, reason);
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}, 'Settle: ' + (promise._label || ' unknown promise'));
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if (!sealed && error) {
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sealed = true;
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_reject(promise, error);
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}
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}, promise);
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}
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function handleOwnThenable(promise, thenable) {
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if (thenable._state === FULFILLED) {
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fulfill(promise, thenable._result);
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} else if (thenable._state === REJECTED) {
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_reject(promise, thenable._result);
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} else {
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subscribe(thenable, undefined, function (value) {
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return _resolve(promise, value);
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}, function (reason) {
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return _reject(promise, reason);
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});
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}
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}
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function handleMaybeThenable(promise, maybeThenable, then$$) {
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if (maybeThenable.constructor === promise.constructor && then$$ === then && maybeThenable.constructor.resolve === resolve) {
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handleOwnThenable(promise, maybeThenable);
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} else {
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if (then$$ === GET_THEN_ERROR) {
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_reject(promise, GET_THEN_ERROR.error);
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} else if (then$$ === undefined) {
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fulfill(promise, maybeThenable);
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} else if (isFunction(then$$)) {
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handleForeignThenable(promise, maybeThenable, then$$);
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} else {
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fulfill(promise, maybeThenable);
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}
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}
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}
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function _resolve(promise, value) {
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if (promise === value) {
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_reject(promise, selfFulfillment());
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} else if (objectOrFunction(value)) {
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handleMaybeThenable(promise, value, getThen(value));
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} else {
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fulfill(promise, value);
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}
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}
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function publishRejection(promise) {
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if (promise._onerror) {
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promise._onerror(promise._result);
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}
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publish(promise);
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}
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function fulfill(promise, value) {
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if (promise._state !== PENDING) {
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return;
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}
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promise._result = value;
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promise._state = FULFILLED;
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if (promise._subscribers.length !== 0) {
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asap(publish, promise);
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}
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}
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function _reject(promise, reason) {
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if (promise._state !== PENDING) {
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return;
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}
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promise._state = REJECTED;
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promise._result = reason;
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asap(publishRejection, promise);
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}
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function subscribe(parent, child, onFulfillment, onRejection) {
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var _subscribers = parent._subscribers;
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var length = _subscribers.length;
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parent._onerror = null;
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_subscribers[length] = child;
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_subscribers[length + FULFILLED] = onFulfillment;
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_subscribers[length + REJECTED] = onRejection;
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if (length === 0 && parent._state) {
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asap(publish, parent);
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}
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}
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function publish(promise) {
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var subscribers = promise._subscribers;
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var settled = promise._state;
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if (subscribers.length === 0) {
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return;
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}
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var child = undefined,
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callback = undefined,
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detail = promise._result;
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for (var i = 0; i < subscribers.length; i += 3) {
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child = subscribers[i];
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callback = subscribers[i + settled];
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if (child) {
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invokeCallback(settled, child, callback, detail);
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} else {
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callback(detail);
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}
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}
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promise._subscribers.length = 0;
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}
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function ErrorObject() {
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this.error = null;
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}
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var TRY_CATCH_ERROR = new ErrorObject();
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function tryCatch(callback, detail) {
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try {
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return callback(detail);
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} catch (e) {
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TRY_CATCH_ERROR.error = e;
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return TRY_CATCH_ERROR;
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}
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}
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function invokeCallback(settled, promise, callback, detail) {
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var hasCallback = isFunction(callback),
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value = undefined,
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error = undefined,
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succeeded = undefined,
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failed = undefined;
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if (hasCallback) {
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value = tryCatch(callback, detail);
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if (value === TRY_CATCH_ERROR) {
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failed = true;
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error = value.error;
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value = null;
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} else {
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succeeded = true;
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}
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if (promise === value) {
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_reject(promise, cannotReturnOwn());
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return;
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}
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} else {
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value = detail;
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succeeded = true;
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}
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if (promise._state !== PENDING) {
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// noop
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} else if (hasCallback && succeeded) {
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_resolve(promise, value);
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} else if (failed) {
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_reject(promise, error);
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} else if (settled === FULFILLED) {
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fulfill(promise, value);
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} else if (settled === REJECTED) {
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_reject(promise, value);
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}
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}
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function initializePromise(promise, resolver) {
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try {
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resolver(function resolvePromise(value) {
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_resolve(promise, value);
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}, function rejectPromise(reason) {
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_reject(promise, reason);
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});
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} catch (e) {
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_reject(promise, e);
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}
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}
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var id = 0;
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function nextId() {
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return id++;
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}
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function makePromise(promise) {
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promise[PROMISE_ID] = id++;
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promise._state = undefined;
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promise._result = undefined;
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promise._subscribers = [];
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}
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function Enumerator(Constructor, input) {
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this._instanceConstructor = Constructor;
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this.promise = new Constructor(noop);
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if (!this.promise[PROMISE_ID]) {
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makePromise(this.promise);
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}
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if (isArray(input)) {
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this._input = input;
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this.length = input.length;
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this._remaining = input.length;
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this._result = new Array(this.length);
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if (this.length === 0) {
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fulfill(this.promise, this._result);
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} else {
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this.length = this.length || 0;
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this._enumerate();
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if (this._remaining === 0) {
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fulfill(this.promise, this._result);
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}
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}
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} else {
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_reject(this.promise, validationError());
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}
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}
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function validationError() {
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return new Error('Array Methods must be provided an Array');
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};
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Enumerator.prototype._enumerate = function () {
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var length = this.length;
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var _input = this._input;
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for (var i = 0; this._state === PENDING && i < length; i++) {
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this._eachEntry(_input[i], i);
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}
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};
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Enumerator.prototype._eachEntry = function (entry, i) {
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var c = this._instanceConstructor;
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var resolve$$ = c.resolve;
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|
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if (resolve$$ === resolve) {
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var _then = getThen(entry);
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|
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if (_then === then && entry._state !== PENDING) {
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this._settledAt(entry._state, i, entry._result);
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} else if (typeof _then !== 'function') {
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this._remaining--;
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this._result[i] = entry;
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} else if (c === Promise) {
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var promise = new c(noop);
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handleMaybeThenable(promise, entry, _then);
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this._willSettleAt(promise, i);
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} else {
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this._willSettleAt(new c(function (resolve$$) {
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return resolve$$(entry);
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}), i);
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}
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} else {
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this._willSettleAt(resolve$$(entry), i);
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}
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};
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|
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Enumerator.prototype._settledAt = function (state, i, value) {
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var promise = this.promise;
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|
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if (promise._state === PENDING) {
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this._remaining--;
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|
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if (state === REJECTED) {
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_reject(promise, value);
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} else {
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this._result[i] = value;
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}
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}
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if (this._remaining === 0) {
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fulfill(promise, this._result);
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}
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};
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Enumerator.prototype._willSettleAt = function (promise, i) {
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var enumerator = this;
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subscribe(promise, undefined, function (value) {
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return enumerator._settledAt(FULFILLED, i, value);
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}, function (reason) {
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return enumerator._settledAt(REJECTED, i, reason);
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});
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};
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|
|
/**
|
|
`Promise.all` accepts an array of promises, and returns a new promise which
|
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is fulfilled with an array of fulfillment values for the passed promises, or
|
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rejected with the reason of the first passed promise to be rejected. It casts all
|
|
elements of the passed iterable to promises as it runs this algorithm.
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|
|
|
Example:
|
|
|
|
```javascript
|
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let promise1 = resolve(1);
|
|
let promise2 = resolve(2);
|
|
let promise3 = resolve(3);
|
|
let promises = [ promise1, promise2, promise3 ];
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|
|
Promise.all(promises).then(function(array){
|
|
// The array here would be [ 1, 2, 3 ];
|
|
});
|
|
```
|
|
|
|
If any of the `promises` given to `all` are rejected, the first promise
|
|
that is rejected will be given as an argument to the returned promises's
|
|
rejection handler. For example:
|
|
|
|
Example:
|
|
|
|
```javascript
|
|
let promise1 = resolve(1);
|
|
let promise2 = reject(new Error("2"));
|
|
let promise3 = reject(new Error("3"));
|
|
let promises = [ promise1, promise2, promise3 ];
|
|
|
|
Promise.all(promises).then(function(array){
|
|
// Code here never runs because there are rejected promises!
|
|
}, function(error) {
|
|
// error.message === "2"
|
|
});
|
|
```
|
|
|
|
@method all
|
|
@static
|
|
@param {Array} entries array of promises
|
|
@param {String} label optional string for labeling the promise.
|
|
Useful for tooling.
|
|
@return {Promise} promise that is fulfilled when all `promises` have been
|
|
fulfilled, or rejected if any of them become rejected.
|
|
@static
|
|
*/
|
|
function all(entries) {
|
|
return new Enumerator(this, entries).promise;
|
|
}
|
|
|
|
/**
|
|
`Promise.race` returns a new promise which is settled in the same way as the
|
|
first passed promise to settle.
|
|
|
|
Example:
|
|
|
|
```javascript
|
|
let promise1 = new Promise(function(resolve, reject){
|
|
setTimeout(function(){
|
|
resolve('promise 1');
|
|
}, 200);
|
|
});
|
|
|
|
let promise2 = new Promise(function(resolve, reject){
|
|
setTimeout(function(){
|
|
resolve('promise 2');
|
|
}, 100);
|
|
});
|
|
|
|
Promise.race([promise1, promise2]).then(function(result){
|
|
// result === 'promise 2' because it was resolved before promise1
|
|
// was resolved.
|
|
});
|
|
```
|
|
|
|
`Promise.race` is deterministic in that only the state of the first
|
|
settled promise matters. For example, even if other promises given to the
|
|
`promises` array argument are resolved, but the first settled promise has
|
|
become rejected before the other promises became fulfilled, the returned
|
|
promise will become rejected:
|
|
|
|
```javascript
|
|
let promise1 = new Promise(function(resolve, reject){
|
|
setTimeout(function(){
|
|
resolve('promise 1');
|
|
}, 200);
|
|
});
|
|
|
|
let promise2 = new Promise(function(resolve, reject){
|
|
setTimeout(function(){
|
|
reject(new Error('promise 2'));
|
|
}, 100);
|
|
});
|
|
|
|
Promise.race([promise1, promise2]).then(function(result){
|
|
// Code here never runs
|
|
}, function(reason){
|
|
// reason.message === 'promise 2' because promise 2 became rejected before
|
|
// promise 1 became fulfilled
|
|
});
|
|
```
|
|
|
|
An example real-world use case is implementing timeouts:
|
|
|
|
```javascript
|
|
Promise.race([ajax('foo.json'), timeout(5000)])
|
|
```
|
|
|
|
@method race
|
|
@static
|
|
@param {Array} promises array of promises to observe
|
|
Useful for tooling.
|
|
@return {Promise} a promise which settles in the same way as the first passed
|
|
promise to settle.
|
|
*/
|
|
function race(entries) {
|
|
/*jshint validthis:true */
|
|
var Constructor = this;
|
|
|
|
if (!isArray(entries)) {
|
|
return new Constructor(function (_, reject) {
|
|
return reject(new TypeError('You must pass an array to race.'));
|
|
});
|
|
} else {
|
|
return new Constructor(function (resolve, reject) {
|
|
var length = entries.length;
|
|
for (var i = 0; i < length; i++) {
|
|
Constructor.resolve(entries[i]).then(resolve, reject);
|
|
}
|
|
});
|
|
}
|
|
}
|
|
|
|
/**
|
|
`Promise.reject` returns a promise rejected with the passed `reason`.
|
|
It is shorthand for the following:
|
|
|
|
```javascript
|
|
let promise = new Promise(function(resolve, reject){
|
|
reject(new Error('WHOOPS'));
|
|
});
|
|
|
|
promise.then(function(value){
|
|
// Code here doesn't run because the promise is rejected!
|
|
}, function(reason){
|
|
// reason.message === 'WHOOPS'
|
|
});
|
|
```
|
|
|
|
Instead of writing the above, your code now simply becomes the following:
|
|
|
|
```javascript
|
|
let promise = Promise.reject(new Error('WHOOPS'));
|
|
|
|
promise.then(function(value){
|
|
// Code here doesn't run because the promise is rejected!
|
|
}, function(reason){
|
|
// reason.message === 'WHOOPS'
|
|
});
|
|
```
|
|
|
|
@method reject
|
|
@static
|
|
@param {Any} reason value that the returned promise will be rejected with.
|
|
Useful for tooling.
|
|
@return {Promise} a promise rejected with the given `reason`.
|
|
*/
|
|
function reject(reason) {
|
|
/*jshint validthis:true */
|
|
var Constructor = this;
|
|
var promise = new Constructor(noop);
|
|
_reject(promise, reason);
|
|
return promise;
|
|
}
|
|
|
|
function needsResolver() {
|
|
throw new TypeError('You must pass a resolver function as the first argument to the promise constructor');
|
|
}
|
|
|
|
function needsNew() {
|
|
throw new TypeError("Failed to construct 'Promise': Please use the 'new' operator, this object constructor cannot be called as a function.");
|
|
}
|
|
|
|
/**
|
|
Promise objects represent the eventual result of an asynchronous operation. The
|
|
primary way of interacting with a promise is through its `then` method, which
|
|
registers callbacks to receive either a promise's eventual value or the reason
|
|
why the promise cannot be fulfilled.
|
|
|
|
Terminology
|
|
-----------
|
|
|
|
- `promise` is an object or function with a `then` method whose behavior conforms to this specification.
|
|
- `thenable` is an object or function that defines a `then` method.
|
|
- `value` is any legal JavaScript value (including undefined, a thenable, or a promise).
|
|
- `exception` is a value that is thrown using the throw statement.
|
|
- `reason` is a value that indicates why a promise was rejected.
|
|
- `settled` the final resting state of a promise, fulfilled or rejected.
|
|
|
|
A promise can be in one of three states: pending, fulfilled, or rejected.
|
|
|
|
Promises that are fulfilled have a fulfillment value and are in the fulfilled
|
|
state. Promises that are rejected have a rejection reason and are in the
|
|
rejected state. A fulfillment value is never a thenable.
|
|
|
|
Promises can also be said to *resolve* a value. If this value is also a
|
|
promise, then the original promise's settled state will match the value's
|
|
settled state. So a promise that *resolves* a promise that rejects will
|
|
itself reject, and a promise that *resolves* a promise that fulfills will
|
|
itself fulfill.
|
|
|
|
|
|
Basic Usage:
|
|
------------
|
|
|
|
```js
|
|
let promise = new Promise(function(resolve, reject) {
|
|
// on success
|
|
resolve(value);
|
|
|
|
// on failure
|
|
reject(reason);
|
|
});
|
|
|
|
promise.then(function(value) {
|
|
// on fulfillment
|
|
}, function(reason) {
|
|
// on rejection
|
|
});
|
|
```
|
|
|
|
Advanced Usage:
|
|
---------------
|
|
|
|
Promises shine when abstracting away asynchronous interactions such as
|
|
`XMLHttpRequest`s.
|
|
|
|
```js
|
|
function getJSON(url) {
|
|
return new Promise(function(resolve, reject){
|
|
let xhr = new XMLHttpRequest();
|
|
|
|
xhr.open('GET', url);
|
|
xhr.onreadystatechange = handler;
|
|
xhr.responseType = 'json';
|
|
xhr.setRequestHeader('Accept', 'application/json');
|
|
xhr.send();
|
|
|
|
function handler() {
|
|
if (this.readyState === this.DONE) {
|
|
if (this.status === 200) {
|
|
resolve(this.response);
|
|
} else {
|
|
reject(new Error('getJSON: `' + url + '` failed with status: [' + this.status + ']'));
|
|
}
|
|
}
|
|
};
|
|
});
|
|
}
|
|
|
|
getJSON('/posts.json').then(function(json) {
|
|
// on fulfillment
|
|
}, function(reason) {
|
|
// on rejection
|
|
});
|
|
```
|
|
|
|
Unlike callbacks, promises are great composable primitives.
|
|
|
|
```js
|
|
Promise.all([
|
|
getJSON('/posts'),
|
|
getJSON('/comments')
|
|
]).then(function(values){
|
|
values[0] // => postsJSON
|
|
values[1] // => commentsJSON
|
|
|
|
return values;
|
|
});
|
|
```
|
|
|
|
@class Promise
|
|
@param {function} resolver
|
|
Useful for tooling.
|
|
@constructor
|
|
*/
|
|
function Promise(resolver) {
|
|
this[PROMISE_ID] = nextId();
|
|
this._result = this._state = undefined;
|
|
this._subscribers = [];
|
|
|
|
if (noop !== resolver) {
|
|
typeof resolver !== 'function' && needsResolver();
|
|
this instanceof Promise ? initializePromise(this, resolver) : needsNew();
|
|
}
|
|
}
|
|
|
|
Promise.all = all;
|
|
Promise.race = race;
|
|
Promise.resolve = resolve;
|
|
Promise.reject = reject;
|
|
Promise._setScheduler = setScheduler;
|
|
Promise._setAsap = setAsap;
|
|
Promise._asap = asap;
|
|
|
|
Promise.prototype = {
|
|
constructor: Promise,
|
|
|
|
/**
|
|
The primary way of interacting with a promise is through its `then` method,
|
|
which registers callbacks to receive either a promise's eventual value or the
|
|
reason why the promise cannot be fulfilled.
|
|
|
|
```js
|
|
findUser().then(function(user){
|
|
// user is available
|
|
}, function(reason){
|
|
// user is unavailable, and you are given the reason why
|
|
});
|
|
```
|
|
|
|
Chaining
|
|
--------
|
|
|
|
The return value of `then` is itself a promise. This second, 'downstream'
|
|
promise is resolved with the return value of the first promise's fulfillment
|
|
or rejection handler, or rejected if the handler throws an exception.
|
|
|
|
```js
|
|
findUser().then(function (user) {
|
|
return user.name;
|
|
}, function (reason) {
|
|
return 'default name';
|
|
}).then(function (userName) {
|
|
// If `findUser` fulfilled, `userName` will be the user's name, otherwise it
|
|
// will be `'default name'`
|
|
});
|
|
|
|
findUser().then(function (user) {
|
|
throw new Error('Found user, but still unhappy');
|
|
}, function (reason) {
|
|
throw new Error('`findUser` rejected and we're unhappy');
|
|
}).then(function (value) {
|
|
// never reached
|
|
}, function (reason) {
|
|
// if `findUser` fulfilled, `reason` will be 'Found user, but still unhappy'.
|
|
// If `findUser` rejected, `reason` will be '`findUser` rejected and we're unhappy'.
|
|
});
|
|
```
|
|
If the downstream promise does not specify a rejection handler, rejection reasons will be propagated further downstream.
|
|
|
|
```js
|
|
findUser().then(function (user) {
|
|
throw new PedagogicalException('Upstream error');
|
|
}).then(function (value) {
|
|
// never reached
|
|
}).then(function (value) {
|
|
// never reached
|
|
}, function (reason) {
|
|
// The `PedgagocialException` is propagated all the way down to here
|
|
});
|
|
```
|
|
|
|
Assimilation
|
|
------------
|
|
|
|
Sometimes the value you want to propagate to a downstream promise can only be
|
|
retrieved asynchronously. This can be achieved by returning a promise in the
|
|
fulfillment or rejection handler. The downstream promise will then be pending
|
|
until the returned promise is settled. This is called *assimilation*.
|
|
|
|
```js
|
|
findUser().then(function (user) {
|
|
return findCommentsByAuthor(user);
|
|
}).then(function (comments) {
|
|
// The user's comments are now available
|
|
});
|
|
```
|
|
|
|
If the assimliated promise rejects, then the downstream promise will also reject.
|
|
|
|
```js
|
|
findUser().then(function (user) {
|
|
return findCommentsByAuthor(user);
|
|
}).then(function (comments) {
|
|
// If `findCommentsByAuthor` fulfills, we'll have the value here
|
|
}, function (reason) {
|
|
// If `findCommentsByAuthor` rejects, we'll have the reason here
|
|
});
|
|
```
|
|
|
|
Simple Example
|
|
--------------
|
|
|
|
Synchronous Example
|
|
|
|
```javascript
|
|
let result;
|
|
|
|
try {
|
|
result = findResult();
|
|
// success
|
|
} catch(reason) {
|
|
// failure
|
|
}
|
|
```
|
|
|
|
Errback Example
|
|
|
|
```js
|
|
findResult(function(result, err){
|
|
if (err) {
|
|
// failure
|
|
} else {
|
|
// success
|
|
}
|
|
});
|
|
```
|
|
|
|
Promise Example;
|
|
|
|
```javascript
|
|
findResult().then(function(result){
|
|
// success
|
|
}, function(reason){
|
|
// failure
|
|
});
|
|
```
|
|
|
|
Advanced Example
|
|
--------------
|
|
|
|
Synchronous Example
|
|
|
|
```javascript
|
|
let author, books;
|
|
|
|
try {
|
|
author = findAuthor();
|
|
books = findBooksByAuthor(author);
|
|
// success
|
|
} catch(reason) {
|
|
// failure
|
|
}
|
|
```
|
|
|
|
Errback Example
|
|
|
|
```js
|
|
|
|
function foundBooks(books) {
|
|
|
|
}
|
|
|
|
function failure(reason) {
|
|
|
|
}
|
|
|
|
findAuthor(function(author, err){
|
|
if (err) {
|
|
failure(err);
|
|
// failure
|
|
} else {
|
|
try {
|
|
findBoooksByAuthor(author, function(books, err) {
|
|
if (err) {
|
|
failure(err);
|
|
} else {
|
|
try {
|
|
foundBooks(books);
|
|
} catch(reason) {
|
|
failure(reason);
|
|
}
|
|
}
|
|
});
|
|
} catch(error) {
|
|
failure(err);
|
|
}
|
|
// success
|
|
}
|
|
});
|
|
```
|
|
|
|
Promise Example;
|
|
|
|
```javascript
|
|
findAuthor().
|
|
then(findBooksByAuthor).
|
|
then(function(books){
|
|
// found books
|
|
}).catch(function(reason){
|
|
// something went wrong
|
|
});
|
|
```
|
|
|
|
@method then
|
|
@param {Function} onFulfilled
|
|
@param {Function} onRejected
|
|
Useful for tooling.
|
|
@return {Promise}
|
|
*/
|
|
then: then,
|
|
|
|
/**
|
|
`catch` is simply sugar for `then(undefined, onRejection)` which makes it the same
|
|
as the catch block of a try/catch statement.
|
|
|
|
```js
|
|
function findAuthor(){
|
|
throw new Error('couldn't find that author');
|
|
}
|
|
|
|
// synchronous
|
|
try {
|
|
findAuthor();
|
|
} catch(reason) {
|
|
// something went wrong
|
|
}
|
|
|
|
// async with promises
|
|
findAuthor().catch(function(reason){
|
|
// something went wrong
|
|
});
|
|
```
|
|
|
|
@method catch
|
|
@param {Function} onRejection
|
|
Useful for tooling.
|
|
@return {Promise}
|
|
*/
|
|
'catch': function _catch(onRejection) {
|
|
return this.then(null, onRejection);
|
|
}
|
|
};
|
|
|
|
function polyfill() {
|
|
var local = undefined;
|
|
|
|
if (typeof global !== 'undefined') {
|
|
local = global;
|
|
} else if (typeof self !== 'undefined') {
|
|
local = self;
|
|
} else {
|
|
try {
|
|
local = Function('return this')();
|
|
} catch (e) {
|
|
throw new Error('polyfill failed because global object is unavailable in this environment');
|
|
}
|
|
}
|
|
|
|
var P = local.Promise;
|
|
|
|
if (P) {
|
|
var promiseToString = null;
|
|
try {
|
|
promiseToString = Object.prototype.toString.call(P.resolve());
|
|
} catch (e) {
|
|
// silently ignored
|
|
}
|
|
|
|
if (promiseToString === '[object Promise]' && !P.cast) {
|
|
return;
|
|
}
|
|
}
|
|
|
|
local.Promise = Promise;
|
|
}
|
|
|
|
// Strange compat..
|
|
Promise.polyfill = polyfill;
|
|
Promise.Promise = Promise;
|
|
|
|
return Promise;
|
|
|
|
})));
|
|
|
|
ES6Promise.polyfill();
|
|
//# sourceMappingURL=es6-promise.auto.map
|