src/promise_polyfill.js

// Promise polyfill from https://github.com/taylorhakes/promise-polyfill
// License:
//==============================================================================
// Copyright (c) 2014 Taylor Hakes
// Copyright (c) 2014 Forbes Lindesay
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
//==============================================================================

/** @suppress{duplicate} This is already defined in from Closure's built-in
    externs.zip//es6.js, Closure should not yell when seeing this again. */
var Promise = (function() {
  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.all = function(arr) {
    return new Promise(function(resolve, reject) {
      if (!Array.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 (!Array.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) {
      setTimeout(fn, 0); // XXX EMSCRIPTEN: just use setTimeout
    };

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

  return Promise;
})();