promise from angularjs

  var defer = function() {
    return new Deferred();
  };

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

  Promise.prototype = {
    then: function(onFulfilled, onRejected, progressBack) {
      var result = new Deferred();

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

      return result.promise;
    },

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

    "finally": function(callback, progressBack) {
      return this.then(function(value) {
        return handleCallback(value, true, callback);
      }, function(error) {
        return handleCallback(error, false, callback);
      }, progressBack);
    }
  };

  //Faster, more basic than angular.bind http://jsperf.com/angular-bind-vs-custom-vs-native
  function simpleBind(context, fn) {
    return function(value) {
      fn.call(context, value);
    };
  }

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

    pending = state.pending;
    state.processScheduled = false;
    state.pending = undefined;
    for (var i = 0, ii = pending.length; i < ii; ++i) {
      promise = pending[i][0];
      fn = pending[i][state.status];
      try {
        if (isFunction(fn)) {
          promise.resolve(fn(state.value));
        } else if (state.status === 1) {
          promise.resolve(state.value);
        } else {
          promise.reject(state.value);
        }
      } catch (e) {
        promise.reject(e);
        exceptionHandler(e);
      }
    }
  }

  function scheduleProcessQueue(state) {
    if (state.processScheduled || !state.pending) return;
    state.processScheduled = true;
    nextTick(function() { processQueue(state); });
  }

  function Deferred() {
    this.promise = new Promise();
    //Necessary to support unbound execution :/
    this.resolve = simpleBind(this, this.resolve);
    this.reject = simpleBind(this, this.reject);
    this.notify = simpleBind(this, this.notify);
  }

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

    },

    $$resolve: function(val) {
      var then, fns;

      fns = callOnce(this, this.$$resolve, this.$$reject);
      try {
        if ((isObject(val) || isFunction(val))) then = val && val.then;
        if (isFunction(then)) {
          this.promise.$$state.status = -1;
          then.call(val, fns[0], fns[1], this.notify);
        } else {
          this.promise.$$state.value = val;
          this.promise.$$state.status = 1;
          scheduleProcessQueue(this.promise.$$state);
        }
      } catch (e) {
        fns[1](e);
        exceptionHandler(e);
      }
    },

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

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

    notify: function(progress) {
      var callbacks = this.promise.$$state.pending;

      if ((this.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 {
              result.notify(isFunction(callback) ? callback(progress) : progress);
            } catch (e) {
              exceptionHandler(e);
            }
          }
        });
      }
    }
  };