Promise.js

/**
@license
Copyright (c) 2016 The Polymer Project Authors. All rights reserved.
This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
Code distributed by Google as part of the polymer project is also
subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
*/
function MakePromise (asap) {
  function Promise(fn) {
		if (typeof this !== 'object' || typeof fn !== 'function') throw new TypeError();
		this._state = null;
		this._value = null;
		this._deferreds = []

		doResolve(fn, resolve.bind(this), reject.bind(this));
	}

	function handle(deferred) {
		var me = this;
		if (this._state === null) {
			this._deferreds.push(deferred);
			return
		}
		asap(function() {
			var cb = me._state ? deferred.onFulfilled : deferred.onRejected
			if (typeof cb !== 'function') {
				(me._state ? deferred.resolve : deferred.reject)(me._value);
				return;
			}
			var ret;
			try {
				ret = cb(me._value);
			}
			catch (e) {
				deferred.reject(e);
				return;
			}
			deferred.resolve(ret);
		})
	}

	function resolve(newValue) {
		try { //Promise Resolution Procedure: https://github.com/promises-aplus/promises-spec#the-promise-resolution-procedure
			if (newValue === this) throw new TypeError();
			if (newValue && (typeof newValue === 'object' || typeof newValue === 'function')) {
				var then = newValue.then;
				if (typeof then === 'function') {
					doResolve(then.bind(newValue), resolve.bind(this), reject.bind(this));
					return;
				}
			}
			this._state = true;
			this._value = newValue;
			finale.call(this);
		} catch (e) { reject.call(this, e); }
	}

	function reject(newValue) {
		this._state = false;
		this._value = newValue;
		finale.call(this);
	}

	function finale() {
		for (var i = 0, len = this._deferreds.length; i < len; i++) {
			handle.call(this, this._deferreds[i]);
		}
		this._deferreds = null;
	}

	/**
	 * Take a potentially misbehaving resolver function and make sure
	 * onFulfilled and onRejected are only called once.
	 *
	 * Makes no guarantees about asynchrony.
	 */
	function doResolve(fn, onFulfilled, onRejected) {
		var done = false;
		try {
			fn(function (value) {
				if (done) return;
				done = true;
				onFulfilled(value);
			}, function (reason) {
				if (done) return;
				done = true;
				onRejected(reason);
			})
		} catch (ex) {
			if (done) return;
			done = true;
			onRejected(ex);
		}
	}

	Promise.prototype['catch'] = function (onRejected) {
		return this.then(null, onRejected);
	};

	Promise.prototype.then = function(onFulfilled, onRejected) {
		var me = this;
		return new Promise(function(resolve, reject) {
      handle.call(me, {
        onFulfilled: onFulfilled,
        onRejected: onRejected,
        resolve: resolve,
        reject: reject
      });
		})
	};

	Promise.resolve = function (value) {
		if (value && typeof value === 'object' && value.constructor === Promise) {
			return value;
		}

		return new Promise(function (resolve) {
			resolve(value);
		});
	};

	Promise.reject = function (value) {
		return new Promise(function (resolve, reject) {
			reject(value);
		});
	};

	
  return Promise;
}

if (typeof module !== 'undefined') {
  module.exports = MakePromise;
}