githubmirror/angular.js

src/ng/q.js
668 строк22 KB
Jason Bedard
refactor($q): separate Promise from Deferred
07 окт 2016, 12:02
07 окт 2016, 12:0234434cf
'use strict';

/**
 * @ngdoc service
 * @name $q
 * @requires $rootScope
 *
 * @description
 * A service that helps you run functions asynchronously, and use their return values (or exceptions)
 * when they are done processing.
 *
 * This is a [Promises/A+](https://promisesaplus.com/)-compliant implementation of promises/deferred
 * objects inspired by [Kris Kowal's Q](https://github.com/kriskowal/q).
 *
 * $q can be used in two fashions --- one which is more similar to Kris Kowal's Q or jQuery's Deferred
 * implementations, and the other which resembles ES6 (ES2015) promises to some degree.
 *
 * # $q constructor
 *
 * The streamlined ES6 style promise is essentially just using $q as a constructor which takes a `resolver`
 * function as the first argument. This is similar to the native Promise implementation from ES6,
 * see [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise).
 *
 * While the constructor-style use is supported, not all of the supporting methods from ES6 promises are
 * available yet.
 *
 * It can be used like so:
 *
 * ```js
 *   // for the purpose of this example let's assume that variables `$q` and `okToGreet`
 *   // are available in the current lexical scope (they could have been injected or passed in).
 *
 *   function asyncGreet(name) {
 *     // perform some asynchronous operation, resolve or reject the promise when appropriate.
 *     return $q(function(resolve, reject) {
 *       setTimeout(function() {
 *         if (okToGreet(name)) {
 *           resolve('Hello, ' + name + '!');
 *         } else {
 *           reject('Greeting ' + name + ' is not allowed.');
 *         }
 *       }, 1000);
 *     });
 *   }
 *
 *   var promise = asyncGreet('Robin Hood');
 *   promise.then(function(greeting) {
 *     alert('Success: ' + greeting);
 *   }, function(reason) {
 *     alert('Failed: ' + reason);
 *   });
 * ```
 *
 * Note: progress/notify callbacks are not currently supported via the ES6-style interface.
 *
 * Note: unlike ES6 behavior, an exception thrown in the constructor function will NOT implicitly reject the promise.
 *
 * However, the more traditional CommonJS-style usage is still available, and documented below.
 *
 * [The CommonJS Promise proposal](http://wiki.commonjs.org/wiki/Promises) describes a promise as an
 * interface for interacting with an object that represents the result of an action that is
 * performed asynchronously, and may or may not be finished at any given point in time.
 *
 * From the perspective of dealing with error handling, deferred and promise APIs are to
 * asynchronous programming what `try`, `catch` and `throw` keywords are to synchronous programming.
 *
 * ```js
 *   // for the purpose of this example let's assume that variables `$q` and `okToGreet`
 *   // are available in the current lexical scope (they could have been injected or passed in).
 *
 *   function asyncGreet(name) {
 *     var deferred = $q.defer();
 *
 *     setTimeout(function() {
 *       deferred.notify('About to greet ' + name + '.');
 *
 *       if (okToGreet(name)) {
 *         deferred.resolve('Hello, ' + name + '!');
 *       } else {
 *         deferred.reject('Greeting ' + name + ' is not allowed.');
 *       }
 *     }, 1000);
 *
 *     return deferred.promise;
 *   }
 *
 *   var promise = asyncGreet('Robin Hood');
 *   promise.then(function(greeting) {
 *     alert('Success: ' + greeting);
 *   }, function(reason) {
 *     alert('Failed: ' + reason);
 *   }, function(update) {
 *     alert('Got notification: ' + update);
 *   });
 * ```
 *
 * At first it might not be obvious why this extra complexity is worth the trouble. The payoff
 * comes in the way of guarantees that promise and deferred APIs make, see
 * https://github.com/kriskowal/uncommonjs/blob/master/promises/specification.md.
 *
 * Additionally the promise api allows for composition that is very hard to do with the
 * traditional callback ([CPS](http://en.wikipedia.org/wiki/Continuation-passing_style)) approach.
 * For more on this please see the [Q documentation](https://github.com/kriskowal/q) especially the
 * section on serial or parallel joining of promises.
 *
 * # The Deferred API
 *
 * A new instance of deferred is constructed by calling `$q.defer()`.
 *
 * The purpose of the deferred object is to expose the associated Promise instance as well as APIs
 * that can be used for signaling the successful or unsuccessful completion, as well as the status
 * of the task.
 *
 * **Methods**
 *
 * - `resolve(value)` – resolves the derived promise with the `value`. If the value is a rejection
 *   constructed via `$q.reject`, the promise will be rejected instead.
 * - `reject(reason)` – rejects the derived promise with the `reason`. This is equivalent to
 *   resolving it with a rejection constructed via `$q.reject`.
 * - `notify(value)` - provides updates on the status of the promise's execution. This may be called
 *   multiple times before the promise is either resolved or rejected.
 *
 * **Properties**
 *
 * - promise – `{Promise}` – promise object associated with this deferred.
 *
 *
 * # The Promise API
 *
 * A new promise instance is created when a deferred instance is created and can be retrieved by
 * calling `deferred.promise`.
 *
 * The purpose of the promise object is to allow for interested parties to get access to the result
 * of the deferred task when it completes.
 *
 * **Methods**
 *
 * - `then(successCallback, [errorCallback], [notifyCallback])` – regardless of when the promise was or
 *   will be resolved or rejected, `then` calls one of the success or error callbacks asynchronously
 *   as soon as the result is available. The callbacks are called with a single argument: the result
 *   or rejection reason. Additionally, the notify callback may be called zero or more times to
 *   provide a progress indication, before the promise is resolved or rejected.
 *
 *   This method *returns a new promise* which is resolved or rejected via the return value of the
 *   `successCallback`, `errorCallback` (unless that value is a promise, in which case it is resolved
 *   with the value which is resolved in that promise using
 *   [promise chaining](http://www.html5rocks.com/en/tutorials/es6/promises/#toc-promises-queues)).
 *   It also notifies via the return value of the `notifyCallback` method. The promise cannot be
 *   resolved or rejected from the notifyCallback method. The errorCallback and notifyCallback
 *   arguments are optional.
 *
 * - `catch(errorCallback)` – shorthand for `promise.then(null, errorCallback)`
 *
 * - `finally(callback, notifyCallback)` – allows you to observe either the fulfillment or rejection of a promise,
 *   but to do so without modifying the final value. This is useful to release resources or do some
 *   clean-up that needs to be done whether the promise was rejected or resolved. See the [full
 *   specification](https://github.com/kriskowal/q/wiki/API-Reference#promisefinallycallback) for
 *   more information.
 *
 * # Chaining promises
 *
 * Because calling the `then` method of a promise returns a new derived promise, it is easily
 * possible to create a chain of promises:
 *
 * ```js
 *   promiseB = promiseA.then(function(result) {
 *     return result + 1;
 *   });
 *
 *   // promiseB will be resolved immediately after promiseA is resolved and its value
 *   // will be the result of promiseA incremented by 1
 * ```
 *
 * It is possible to create chains of any length and since a promise can be resolved with another
 * promise (which will defer its resolution further), it is possible to pause/defer resolution of
 * the promises at any point in the chain. This makes it possible to implement powerful APIs like
 * $http's response interceptors.
 *
 *
 * # Differences between Kris Kowal's Q and $q
 *
 *  There are two main differences:
 *
 * - $q is integrated with the {@link ng.$rootScope.Scope} Scope model observation
 *   mechanism in angular, which means faster propagation of resolution or rejection into your
 *   models and avoiding unnecessary browser repaints, which would result in flickering UI.
 * - Q has many more features than $q, but that comes at a cost of bytes. $q is tiny, but contains
 *   all the important functionality needed for common async tasks.
 *
 * # Testing
 *
 *  ```js
 *    it('should simulate promise', inject(function($q, $rootScope) {
 *      var deferred = $q.defer();
 *      var promise = deferred.promise;
 *      var resolvedValue;
 *
 *      promise.then(function(value) { resolvedValue = value; });
 *      expect(resolvedValue).toBeUndefined();
 *
 *      // Simulate resolving of promise
 *      deferred.resolve(123);
 *      // Note that the 'then' function does not get called synchronously.
 *      // This is because we want the promise API to always be async, whether or not
 *      // it got called synchronously or asynchronously.
 *      expect(resolvedValue).toBeUndefined();
 *
 *      // Propagate promise resolution to 'then' functions using $apply().
 *      $rootScope.$apply();
 *      expect(resolvedValue).toEqual(123);
 *    }));
 *  ```
 *
 * @param {function(function, function)} resolver Function which is responsible for resolving or
 *   rejecting the newly created promise. The first parameter is a function which resolves the
 *   promise, the second parameter is a function which rejects the promise.
 *
 * @returns {Promise} The newly created promise.
 */
/**
 * @ngdoc provider
 * @name $qProvider
 * @this
 *
 * @description
 */
function $QProvider() {
  var errorOnUnhandledRejections = true;
  this.$get = ['$rootScope', '$exceptionHandler', function($rootScope, $exceptionHandler) {
    return qFactory(function(callback) {
      $rootScope.$evalAsync(callback);
    }, $exceptionHandler, errorOnUnhandledRejections);
  }];

  /**
   * @ngdoc method
   * @name $qProvider#errorOnUnhandledRejections
   * @kind function
   *
   * @description
   * Retrieves or overrides whether to generate an error when a rejected promise is not handled.
   *
   * @param {boolean=} value Whether to generate an error when a rejected promise is not handled.
   * @returns {boolean|ng.$qProvider} Current value when called without a new value or self for
   *    chaining otherwise.
   */
  this.errorOnUnhandledRejections = function(value) {
    if (isDefined(value)) {
      errorOnUnhandledRejections = value;
      return this;
    } else {
      return errorOnUnhandledRejections;
    }
  };
}

/** @this */
function $$QProvider() {
  var errorOnUnhandledRejections = true;
  this.$get = ['$browser', '$exceptionHandler', function($browser, $exceptionHandler) {
    return qFactory(function(callback) {
      $browser.defer(callback);
    }, $exceptionHandler, errorOnUnhandledRejections);
  }];

  this.errorOnUnhandledRejections = function(value) {
    if (isDefined(value)) {
      errorOnUnhandledRejections = value;
      return this;
    } else {
      return errorOnUnhandledRejections;
    }
  };
}

/**
 * Constructs a promise manager.
 *
 * @param {function(function)} nextTick Function for executing functions in the next turn.
 * @param {function(...*)} exceptionHandler Function into which unexpected exceptions are passed for
 *     debugging purposes.
 @ param {=boolean} errorOnUnhandledRejections Whether an error should be generated on unhandled
 *     promises rejections.
 * @returns {object} Promise manager.
 */
function qFactory(nextTick, exceptionHandler, errorOnUnhandledRejections) {
  var $qMinErr = minErr('$q', TypeError);
  var queueSize = 0;
  var checkQueue = [];

  /**
   * @ngdoc method
   * @name ng.$q#defer
   * @kind function
   *
   * @description
   * Creates a `Deferred` object which represents a task which will finish in the future.
   *
   * @returns {Deferred} Returns a new instance of deferred.
   */
  function defer() {
    return new Deferred();
  }

  function Deferred() {
    var promise = this.promise = new Promise();
    //Non prototype methods necessary to support unbound execution :/
    this.resolve = function(val) { resolvePromise(promise, val); };
    this.reject = function(reason) { rejectPromise(promise, reason); };
    this.notify = function(progress) { notifyPromise(promise, progress); };
  }


  function Promise() {
    this.$$state = { status: 0 };
  }

  extend(Promise.prototype, {
    then: function(onFulfilled, onRejected, progressBack) {
      if (isUndefined(onFulfilled) && isUndefined(onRejected) && isUndefined(progressBack)) {
        return this;
      }
      var result = new Promise();

      this.$$state.pending = this.$$state.pending || [];
      this.$$state.pending.push([result, onFulfilled, onRejected, progressBack]);
      if (this.$$state.status > 0) scheduleProcessQueue(this.$$state);

      return result;
    },

    'catch': function(callback) {
      return this.then(null, callback);
    },

    'finally': function(callback, progressBack) {
      return this.then(function(value) {
        return handleCallback(value, resolve, callback);
      }, function(error) {
        return handleCallback(error, reject, callback);
      }, progressBack);
    }
  });

  function processQueue(state) {
    var fn, promise, pending;

    pending = state.pending;
    state.processScheduled = false;
    state.pending = undefined;
    try {
      for (var i = 0, ii = pending.length; i < ii; ++i) {
        state.pur = true;
        promise = pending[i][0];
        fn = pending[i][state.status];
        try {
          if (isFunction(fn)) {
            resolvePromise(promise, fn(state.value));
          } else if (state.status === 1) {
            resolvePromise(promise, state.value);
          } else {
            rejectPromise(promise, state.value);
          }
        } catch (e) {
          rejectPromise(promise, e);
        }
      }
    } finally {
      --queueSize;
      if (errorOnUnhandledRejections && queueSize === 0) {
        nextTick(processChecks);
      }
    }
  }

  function processChecks() {
    // eslint-disable-next-line no-unmodified-loop-condition
    while (!queueSize && checkQueue.length) {
      var toCheck = checkQueue.shift();
      if (!toCheck.pur) {
        toCheck.pur = true;
        var errorMessage = 'Possibly unhandled rejection: ' + toDebugString(toCheck.value);
        exceptionHandler(errorMessage);
      }
    }
  }

  function scheduleProcessQueue(state) {
    if (errorOnUnhandledRejections && !state.pending && state.status === 2 && !state.pur) {
      if (queueSize === 0 && checkQueue.length === 0) {
        nextTick(processChecks);
      }
      checkQueue.push(state);
    }
    if (state.processScheduled || !state.pending) return;
    state.processScheduled = true;
    ++queueSize;
    nextTick(function() { processQueue(state); });
  }

  function resolvePromise(promise, val) {
    if (promise.$$state.status) return;
    if (val === promise) {
      $$reject(promise, $qMinErr(
        'qcycle',
        'Expected promise to be resolved with value other than itself \'{0}\'',
        val));
    } else {
      $$resolve(promise, val);
    }

  }

  function $$resolve(promise, val) {
    var then;
    var done = false;
    try {
      if (isObject(val) || isFunction(val)) then = val.then;
      if (isFunction(then)) {
        promise.$$state.status = -1;
        then.call(val, doResolve, doReject, doNotify);
      } else {
        promise.$$state.value = val;
        promise.$$state.status = 1;
        scheduleProcessQueue(promise.$$state);
      }
    } catch (e) {
      doReject(e);
    }

    function doResolve(val) {
      if (done) return;
      done = true;
      $$resolve(promise, val);
    }
    function doReject(val) {
      if (done) return;
      done = true;
      $$reject(promise, val);
    }
    function doNotify(progress) {
      notifyPromise(promise, progress);
    }
  }

  function rejectPromise(promise, reason) {
    if (promise.$$state.status) return;
    $$reject(promise, reason);
  }

  function $$reject(promise, reason) {
    promise.$$state.value = reason;
    promise.$$state.status = 2;
    scheduleProcessQueue(promise.$$state);
  }

  function notifyPromise(promise, progress) {
    var callbacks = promise.$$state.pending;

    if ((promise.$$state.status <= 0) && callbacks && callbacks.length) {
      nextTick(function() {
        var callback, result;
        for (var i = 0, ii = callbacks.length; i < ii; i++) {
          result = callbacks[i][0];
          callback = callbacks[i][3];
          try {
            notifyPromise(result, isFunction(callback) ? callback(progress) : progress);
          } catch (e) {
            exceptionHandler(e);
          }
        }
      });
    }
  }

  /**
   * @ngdoc method
   * @name $q#reject
   * @kind function
   *
   * @description
   * Creates a promise that is resolved as rejected with the specified `reason`. This api should be
   * used to forward rejection in a chain of promises. If you are dealing with the last promise in
   * a promise chain, you don't need to worry about it.
   *
   * When comparing deferreds/promises to the familiar behavior of try/catch/throw, think of
   * `reject` as the `throw` keyword in JavaScript. This also means that if you "catch" an error via
   * a promise error callback and you want to forward the error to the promise derived from the
   * current promise, you have to "rethrow" the error by returning a rejection constructed via
   * `reject`.
   *
   * ```js
   *   promiseB = promiseA.then(function(result) {
   *     // success: do something and resolve promiseB
   *     //          with the old or a new result
   *     return result;
   *   }, function(reason) {
   *     // error: handle the error if possible and
   *     //        resolve promiseB with newPromiseOrValue,
   *     //        otherwise forward the rejection to promiseB
   *     if (canHandle(reason)) {
   *      // handle the error and recover
   *      return newPromiseOrValue;
   *     }
   *     return $q.reject(reason);
   *   });
   * ```
   *
   * @param {*} reason Constant, message, exception or an object representing the rejection reason.
   * @returns {Promise} Returns a promise that was already resolved as rejected with the `reason`.
   */
  function reject(reason) {
    var result = new Promise();
    rejectPromise(result, reason);
    return result;
  }

  function handleCallback(value, resolver, callback) {
    var callbackOutput = null;
    try {
      if (isFunction(callback)) callbackOutput = callback();
    } catch (e) {
      return reject(e);
    }
    if (isPromiseLike(callbackOutput)) {
      return callbackOutput.then(function() {
        return resolver(value);
      }, reject);
    } else {
      return resolver(value);
    }
  }

  /**
   * @ngdoc method
   * @name $q#when
   * @kind function
   *
   * @description
   * Wraps an object that might be a value or a (3rd party) then-able promise into a $q promise.
   * This is useful when you are dealing with an object that might or might not be a promise, or if
   * the promise comes from a source that can't be trusted.
   *
   * @param {*} value Value or a promise
   * @param {Function=} successCallback
   * @param {Function=} errorCallback
   * @param {Function=} progressCallback
   * @returns {Promise} Returns a promise of the passed value or promise
   */


  function when(value, callback, errback, progressBack) {
    var result = new Promise();
    resolvePromise(result, value);
    return result.then(callback, errback, progressBack);
  }

  /**
   * @ngdoc method
   * @name $q#resolve
   * @kind function
   *
   * @description
   * Alias of {@link ng.$q#when when} to maintain naming consistency with ES6.
   *
   * @param {*} value Value or a promise
   * @param {Function=} successCallback
   * @param {Function=} errorCallback
   * @param {Function=} progressCallback
   * @returns {Promise} Returns a promise of the passed value or promise
   */
  var resolve = when;

  /**
   * @ngdoc method
   * @name $q#all
   * @kind function
   *
   * @description
   * Combines multiple promises into a single promise that is resolved when all of the input
   * promises are resolved.
   *
   * @param {Array.<Promise>|Object.<Promise>} promises An array or hash of promises.
   * @returns {Promise} Returns a single promise that will be resolved with an array/hash of values,
   *   each value corresponding to the promise at the same index/key in the `promises` array/hash.
   *   If any of the promises is resolved with a rejection, this resulting promise will be rejected
   *   with the same rejection value.
   */

  function all(promises) {
    var result = new Promise(),
        counter = 0,
        results = isArray(promises) ? [] : {};

    forEach(promises, function(promise, key) {
      counter++;
      when(promise).then(function(value) {
        results[key] = value;
        if (!(--counter)) resolvePromise(result, results);
      }, function(reason) {
        rejectPromise(result, reason);
      });
    });

    if (counter === 0) {
      resolvePromise(result, results);
    }

    return result;
  }

  /**
   * @ngdoc method
   * @name $q#race
   * @kind function
   *
   * @description
   * Returns a promise that resolves or rejects as soon as one of those promises
   * resolves or rejects, with the value or reason from that promise.
   *
   * @param {Array.<Promise>|Object.<Promise>} promises An array or hash of promises.
   * @returns {Promise} a promise that resolves or rejects as soon as one of the `promises`
   * resolves or rejects, with the value or reason from that promise.
   */

  function race(promises) {
    var deferred = defer();

    forEach(promises, function(promise) {
      when(promise).then(deferred.resolve, deferred.reject);
    });

    return deferred.promise;
  }

  function $Q(resolver) {
    if (!isFunction(resolver)) {
      throw $qMinErr('norslvr', 'Expected resolverFn, got \'{0}\'', resolver);
    }

    var promise = new Promise();

    function resolveFn(value) {
      resolvePromise(promise, value);
    }

    function rejectFn(reason) {
      rejectPromise(promise, reason);
    }

    resolver(resolveFn, rejectFn);

    return promise;
  }

  // Let's make the instanceof operator work for promises, so that
  // `new $q(fn) instanceof $q` would evaluate to true.
  $Q.prototype = Promise.prototype;

  $Q.defer = defer;
  $Q.reject = reject;
  $Q.when = when;
  $Q.resolve = resolve;
  $Q.all = all;
  $Q.race = race;

  return $Q;
}