Skip to main content Accessibility Feedback

Promise()

Pushes support back to IE9.

/**
 * Promise Polyfill
 * https://github.com/taylorhakes/promise-polyfill
 * (c) Taylor Hakes, MIT License
 */
(function (global, factory) {
	typeof exports === 'object' && typeof module !== 'undefined' ? factory() :
	typeof define === 'function' && define.amd ? define(factory) :
	(factory());
}(this, (function () { 'use strict';

	/**
	 * @this {Promise}
	 */
	function finallyConstructor(callback) {
	  var constructor = this.constructor;
	  return this.then(
	    function(value) {
	      // @ts-ignore
	      return constructor.resolve(callback()).then(function() {
	        return value;
	      });
	    },
	    function(reason) {
	      // @ts-ignore
	      return constructor.resolve(callback()).then(function() {
	        // @ts-ignore
	        return constructor.reject(reason);
	      });
	    }
	  );
	}

	// Store setTimeout reference so promise-polyfill will be unaffected by
	// other code modifying setTimeout (like sinon.useFakeTimers())
	var setTimeoutFunc = setTimeout;

	function isArray(x) {
	  return Boolean(x && typeof x.length !== 'undefined');
	}

	function noop() {}

	// Polyfill for Function.prototype.bind
	function bind(fn, thisArg) {
	  return function() {
	    fn.apply(thisArg, arguments);
	  };
	}

	/**
	 * @constructor
	 * @param {Function} fn
	 */
	function Promise(fn) {
	  if (!(this instanceof Promise))
	    throw new TypeError('Promises must be constructed via new');
	  if (typeof fn !== 'function') throw new TypeError('not a function');
	  /** @type {!number} */
	  this._state = 0;
	  /** @type {!boolean} */
	  this._handled = false;
	  /** @type {Promise|undefined} */
	  this._value = undefined;
	  /** @type {!Array<!Function>} */
	  this._deferreds = [];

	  doResolve(fn, this);
	}

	function handle(self, deferred) {
	  while (self._state === 3) {
	    self = self._value;
	  }
	  if (self._state === 0) {
	    self._deferreds.push(deferred);
	    return;
	  }
	  self._handled = true;
	  Promise._immediateFn(function() {
	    var cb = self._state === 1 ? deferred.onFulfilled : deferred.onRejected;
	    if (cb === null) {
	      (self._state === 1 ? resolve : reject)(deferred.promise, self._value);
	      return;
	    }
	    var ret;
	    try {
	      ret = cb(self._value);
	    } catch (e) {
	      reject(deferred.promise, e);
	      return;
	    }
	    resolve(deferred.promise, ret);
	  });
	}

	function resolve(self, newValue) {
	  try {
	    // Promise Resolution Procedure: https://github.com/promises-aplus/promises-spec#the-promise-resolution-procedure
	    if (newValue === self)
	      throw new TypeError('A promise cannot be resolved with itself.');
	    if (
	      newValue &&
	      (typeof newValue === 'object' || typeof newValue === 'function')
	    ) {
	      var then = newValue.then;
	      if (newValue instanceof Promise) {
	        self._state = 3;
	        self._value = newValue;
	        finale(self);
	        return;
	      } else if (typeof then === 'function') {
	        doResolve(bind(then, newValue), self);
	        return;
	      }
	    }
	    self._state = 1;
	    self._value = newValue;
	    finale(self);
	  } catch (e) {
	    reject(self, e);
	  }
	}

	function reject(self, newValue) {
	  self._state = 2;
	  self._value = newValue;
	  finale(self);
	}

	function finale(self) {
	  if (self._state === 2 && self._deferreds.length === 0) {
	    Promise._immediateFn(function() {
	      if (!self._handled) {
	        Promise._unhandledRejectionFn(self._value);
	      }
	    });
	  }

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

	/**
	 * @constructor
	 */
	function Handler(onFulfilled, onRejected, promise) {
	  this.onFulfilled = typeof onFulfilled === 'function' ? onFulfilled : null;
	  this.onRejected = typeof onRejected === 'function' ? onRejected : null;
	  this.promise = promise;
	}

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

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

	Promise.prototype.then = function(onFulfilled, onRejected) {
	  // @ts-ignore
	  var prom = new this.constructor(noop);

	  handle(this, new Handler(onFulfilled, onRejected, prom));
	  return prom;
	};

	Promise.prototype['finally'] = finallyConstructor;

	Promise.all = function(arr) {
	  return new Promise(function(resolve, reject) {
	    if (!isArray(arr)) {
	      return reject(new TypeError('Promise.all accepts an array'));
	    }

	    var args = Array.prototype.slice.call(arr);
	    if (args.length === 0) return resolve([]);
	    var remaining = args.length;

	    function res(i, val) {
	      try {
	        if (val && (typeof val === 'object' || typeof val === 'function')) {
	          var then = val.then;
	          if (typeof then === 'function') {
	            then.call(
	              val,
	              function(val) {
	                res(i, val);
	              },
	              reject
	            );
	            return;
	          }
	        }
	        args[i] = val;
	        if (--remaining === 0) {
	          resolve(args);
	        }
	      } catch (ex) {
	        reject(ex);
	      }
	    }

	    for (var i = 0; i < args.length; i++) {
	      res(i, args[i]);
	    }
	  });
	};

	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);
	  });
	};

	Promise.race = function(arr) {
	  return new Promise(function(resolve, reject) {
	    if (!isArray(arr)) {
	      return reject(new TypeError('Promise.race accepts an array'));
	    }

	    for (var i = 0, len = arr.length; i < len; i++) {
	      Promise.resolve(arr[i]).then(resolve, reject);
	    }
	  });
	};

	// Use polyfill for setImmediate for performance gains
	Promise._immediateFn =
	  // @ts-ignore
	  (typeof setImmediate === 'function' &&
	    function(fn) {
	      // @ts-ignore
	      setImmediate(fn);
	    }) ||
	  function(fn) {
	    setTimeoutFunc(fn, 0);
	  };

	Promise._unhandledRejectionFn = function _unhandledRejectionFn(err) {
	  if (typeof console !== 'undefined' && console) {
	    console.warn('Possible Unhandled Promise Rejection:', err); // eslint-disable-line no-console
	  }
	};

	/** @suppress {undefinedVars} */
	var globalNS = (function() {
	  // the only reliable means to get the global object is
	  // `Function('return this')()`
	  // However, this causes CSP violations in Chrome apps.
	  if (typeof self !== 'undefined') {
	    return self;
	  }
	  if (typeof window !== 'undefined') {
	    return window;
	  }
	  if (typeof global !== 'undefined') {
	    return global;
	  }
	  throw new Error('unable to locate global object');
	})();

	if (!('Promise' in globalNS)) {
	  globalNS['Promise'] = Promise;
	} else if (!globalNS.Promise.prototype['finally']) {
	  globalNS.Promise.prototype['finally'] = finallyConstructor;
	}

})));