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410 lines
10 KiB
JavaScript
410 lines
10 KiB
JavaScript
/*
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* Copyright 2009-2011 Mozilla Foundation and contributors
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* Licensed under the New BSD license. See LICENSE.txt or:
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* http://opensource.org/licenses/BSD-3-Clause
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*/
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var EXPORTED_SYMBOLS = [ "Promise" ];
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/**
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* Create an unfulfilled promise
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*
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* @param {*=} aTrace A debugging value
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*
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* @constructor
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*/
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function Promise(aTrace) {
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this._status = Promise.PENDING;
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this._value = undefined;
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this._onSuccessHandlers = [];
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this._onErrorHandlers = [];
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this._trace = aTrace;
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// Debugging help
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if (Promise.Debug._debug) {
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this._id = Promise.Debug._nextId++;
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Promise.Debug._outstanding[this._id] = this;
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}
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}
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/**
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* Debugging options and tools.
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*/
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Promise.Debug = {
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/**
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* Set current debugging mode.
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*
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* @param {boolean} value If |true|, maintain _nextId, _outstanding, _recent.
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* Otherwise, cleanup debugging data.
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*/
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setDebug: function(value) {
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Promise.Debug._debug = value;
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if (!value) {
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Promise.Debug._outstanding = [];
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Promise.Debug._recent = [];
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}
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},
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_debug: false,
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/**
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* We give promises and ID so we can track which are outstanding.
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*/
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_nextId: 0,
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/**
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* Outstanding promises. Handy for debugging (only).
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*/
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_outstanding: [],
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/**
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* Recently resolved promises. Also for debugging only.
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*/
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_recent: []
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};
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/**
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* A promise can be in one of 2 states.
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* The ERROR and SUCCESS states are terminal, the PENDING state is the only
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* start state.
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*/
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Promise.ERROR = -1;
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Promise.PENDING = 0;
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Promise.SUCCESS = 1;
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/**
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* Yeay for RTTI
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*/
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Promise.prototype.isPromise = true;
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/**
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* Have we either been resolve()ed or reject()ed?
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*/
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Promise.prototype.isComplete = function() {
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return this._status != Promise.PENDING;
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};
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/**
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* Have we resolve()ed?
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*/
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Promise.prototype.isResolved = function() {
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return this._status == Promise.SUCCESS;
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};
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/**
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* Have we reject()ed?
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*/
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Promise.prototype.isRejected = function() {
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return this._status == Promise.ERROR;
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};
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/**
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* Take the specified action of fulfillment of a promise, and (optionally)
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* a different action on promise rejection
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*/
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Promise.prototype.then = function(onSuccess, onError) {
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if (typeof onSuccess === 'function') {
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if (this._status === Promise.SUCCESS) {
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onSuccess.call(null, this._value);
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}
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else if (this._status === Promise.PENDING) {
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this._onSuccessHandlers.push(onSuccess);
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}
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}
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if (typeof onError === 'function') {
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if (this._status === Promise.ERROR) {
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onError.call(null, this._value);
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}
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else if (this._status === Promise.PENDING) {
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this._onErrorHandlers.push(onError);
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}
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}
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return this;
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};
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/**
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* Like then() except that rather than returning <tt>this</tt> we return
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* a promise which resolves when the original promise resolves
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*/
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Promise.prototype.chainPromise = function(onSuccess) {
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var chain = new Promise();
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chain._chainedFrom = this;
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this.then(function(data) {
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try {
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chain.resolve(onSuccess(data));
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}
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catch (ex) {
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chain.reject(ex);
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}
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}, function(ex) {
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chain.reject(ex);
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});
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return chain;
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};
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/**
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* Supply the fulfillment of a promise
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*/
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Promise.prototype.resolve = function(data) {
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return this._complete(this._onSuccessHandlers,
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Promise.SUCCESS, data, 'resolve');
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};
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/**
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* Renege on a promise
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*/
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Promise.prototype.reject = function(data) {
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return this._complete(this._onErrorHandlers, Promise.ERROR, data, 'reject');
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};
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/**
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* Internal method to be called on resolve() or reject()
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* @private
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*/
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Promise.prototype._complete = function(list, status, data, name) {
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// Complain if we've already been completed
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if (this._status != Promise.PENDING) {
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Promise._error("Promise complete.", "Attempted ", name, "() with ", data);
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Promise._error("Previous status: ", this._status, ", value =", this._value);
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throw new Error('Promise already complete');
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}
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if (list.length == 0 && status == Promise.ERROR) {
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var frame;
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var text;
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//Complain if a rejection is ignored
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//(this is the equivalent of an empty catch-all clause)
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Promise._error("Promise rejection ignored and silently dropped", data);
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if (data.stack) {// This looks like an exception. Try harder to display it
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if (data.fileName && data.lineNumber) {
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Promise._error("Error originating at", data.fileName,
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", line", data.lineNumber );
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}
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try {
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for (frame = data.stack; frame; frame = frame.caller) {
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text += frame + "\n";
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}
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Promise._error("Attempting to extract exception stack", text);
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} catch (x) {
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Promise._error("Could not extract exception stack.");
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}
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} else {
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Promise._error("Exception stack not available.");
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}
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if (Components && Components.stack) {
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try {
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text = "";
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for (frame = Components.stack; frame; frame = frame.caller) {
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text += frame + "\n";
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}
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Promise._error("Attempting to extract current stack", text);
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} catch (x) {
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Promise._error("Could not extract current stack.");
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}
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} else {
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Promise._error("Current stack not available.");
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}
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}
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this._status = status;
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this._value = data;
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// Call all the handlers, and then delete them
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list.forEach(function(handler) {
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handler.call(null, this._value);
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}, this);
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delete this._onSuccessHandlers;
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delete this._onErrorHandlers;
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// Remove the given {promise} from the _outstanding list, and add it to the
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// _recent list, pruning more than 20 recent promises from that list
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delete Promise.Debug._outstanding[this._id];
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// The original code includes this very useful debugging aid, however there
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// is concern that it will create a memory leak, so we leave it out here.
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/*
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Promise._recent.push(this);
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while (Promise._recent.length > 20) {
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Promise._recent.shift();
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}
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*/
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return this;
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};
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/**
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* Log an error on the most appropriate channel.
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*
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* If the console is available, this method uses |console.warn|. Otherwise,
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* this method falls back to |dump|.
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*
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* @param {...*} items Items to log.
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*/
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Promise._error = null;
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if (typeof console != "undefined" && console.warn) {
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Promise._error = function() {
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var args = Array.prototype.slice.call(arguments);
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args.unshift("Promise");
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console.warn.call(console, args);
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};
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} else {
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Promise._error = function() {
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var i;
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var len = arguments.length;
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dump("Promise: ");
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for (i = 0; i < len; ++i) {
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dump(arguments[i]+" ");
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}
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dump("\n");
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};
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}
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/**
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* Takes an array of promises and returns a promise that that is fulfilled once
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* all the promises in the array are fulfilled
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* @param promiseList The array of promises
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* @return the promise that is fulfilled when all the array is fulfilled
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*/
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Promise.group = function(promiseList) {
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if (!Array.isArray(promiseList)) {
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promiseList = Array.prototype.slice.call(arguments);
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}
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// If the original array has nothing in it, return now to avoid waiting
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if (promiseList.length === 0) {
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return new Promise().resolve([]);
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}
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var groupPromise = new Promise();
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var results = [];
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var fulfilled = 0;
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var onSuccessFactory = function(index) {
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return function(data) {
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results[index] = data;
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fulfilled++;
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// If the group has already failed, silently drop extra results
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if (groupPromise._status !== Promise.ERROR) {
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if (fulfilled === promiseList.length) {
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groupPromise.resolve(results);
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}
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}
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};
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};
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promiseList.forEach(function(promise, index) {
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var onSuccess = onSuccessFactory(index);
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var onError = groupPromise.reject.bind(groupPromise);
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promise.then(onSuccess, onError);
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});
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return groupPromise;
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};
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/**
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* Trap errors.
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*
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* This function serves as an asynchronous counterpart to |catch|.
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*
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* Example:
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* myPromise.chainPromise(a) //May reject
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* .chainPromise(b) //May reject
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* .chainPromise(c) //May reject
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* .trap(d) //Catch any rejection from a, b or c
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* .chainPromise(e) //If either a, b and c or
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* //d has resolved, execute
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*
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* Scenario 1:
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* If a, b, c resolve, e is executed as if d had not been added.
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*
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* Scenario 2:
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* If a, b or c rejects, d is executed. If d resolves, we proceed
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* with e as if nothing had happened. Otherwise, we proceed with
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* the rejection of d.
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*
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* @param {Function} aTrap Called if |this| promise is rejected,
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* with one argument: the rejection.
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* @return {Promise} A new promise. This promise resolves if all
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* previous promises have resolved or if |aTrap| succeeds.
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*/
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Promise.prototype.trap = function(aTrap) {
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var promise = new Promise();
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var resolve = Promise.prototype.resolve.bind(promise);
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var reject = function(aRejection) {
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try {
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//Attempt to handle issue
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var result = aTrap.call(aTrap, aRejection);
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promise.resolve(result);
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} catch (x) {
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promise.reject(x);
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}
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};
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this.then(resolve, reject);
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return promise;
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};
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/**
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* Execute regardless of errors.
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*
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* This function serves as an asynchronous counterpart to |finally|.
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*
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* Example:
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* myPromise.chainPromise(a) //May reject
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* .chainPromise(b) //May reject
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* .chainPromise(c) //May reject
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* .always(d) //Executed regardless
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* .chainPromise(e)
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*
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* Whether |a|, |b| or |c| resolve or reject, |d| is executed.
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*
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* @param {Function} aTrap Called regardless of whether |this|
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* succeeds or fails.
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* @return {Promise} A new promise. This promise holds the same
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* resolution/rejection as |this|.
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*/
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Promise.prototype.always = function(aTrap) {
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var promise = new Promise();
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var resolve = function(result) {
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try {
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aTrap.call(aTrap);
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promise.resolve(result);
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} catch (x) {
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promise.reject(x);
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}
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};
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var reject = function(result) {
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try {
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aTrap.call(aTrap);
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promise.reject(result);
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} catch (x) {
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promise.reject(result);
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}
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};
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this.then(resolve, reject);
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return promise;
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};
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Promise.prototype.toString = function() {
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var status;
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switch (this._status) {
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case Promise.PENDING:
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status = "pending";
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break;
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case Promise.SUCCESS:
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status = "resolved";
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break;
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case Promise.ERROR:
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status = "rejected";
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break;
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default:
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status = "invalid status: "+this._status;
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}
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return "[Promise " + this._id + " (" + status + ")]";
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};
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