javascript PRomise 学习 (中)

时隔多日，对promise有了多一点点的了解。

最近用angularjs 做开发，所以研究了一下它的 $q

功能不算很强大，算是简化版的 Q.js

参考了一下源码，不过我的等级还差很多...

作为学习，我自己又重写了一篇。

这次的比较整齐。代码也少了 .

        $q = function (asyncFn) {            var defer = new Deferred();            asyncFn(defer.resolve.bind(defer), defer.reject.bind(defer));            return defer.promise;        };        $q.defer = function () {            return new Deferred();        };        $q.reject = function (reason) {            var defer = new Deferred();            defer.reject(reason);            return defer.promise;        };        $q.all = function (values) {                        var defer = new Deferred();            var finalDatas = [];            var count = 0;            values.forEach(function (value, i) {                count++;                $q.when(value, function (data) {                    finalDatas[i] = data; //直接按index装入，不用另外排序                    if (--count === 0) { //一个++ 一个-- 互相抵消                        defer.resolve(finalDatas);                    }                }, function (reason) {                    defer.reject(reason);                });            });            return defer.promise;        };        $q.when = function (value, onFulfilled, onRejected, onNotify) {                        if (value instanceof Promise) return value.then(onFulfilled, onRejected, onNotify);                       var defer = new Deferred();            defer.resolve(value);            return defer.promise.then(onFulfilled, onRejected, onNotify);                  };        function Deferred() {            this.promise = new Promise();        }        Deferred.prototype = {            //resolve reject 几乎是一样的， notify 在调用后不会被删除            resolve: function (data) {                var promise = this.promise;                //要延误执行,防止then方法还没有设置好回调,就想要resolve的情况                setTimeout(function () {                                      promise.states = "fulfilled";                    promise._processCallback(data);                }, 0);            },            reject: function (reason) {                var promise = this.promise;                setTimeout(function () {                                     promise.states = "rejected";                    promise._processCallback(reason);                }, 0);            },            notify: function (data) {                var promise = this.promise;                setTimeout(function () {                                     promise.states = "notify";                    promise._processCallback(data, true);                }, 0);            },            constructor: Deferred        }        //主要是保存defer, 做promise连用        function Callback(defer, onFulfilled, onRejected, onNotify) {            this.defer = defer;            this.onFulfilled = onFulfilled;            this.onRejected = onRejected;            this.onNotify = onNotify;        }        function Promise() {            this.states = "pending";            this.value = undefined;            this.reason = undefined;            this._callbacks = [];        }        Promise.prototype = {            then: function (onFulfilled, onRejected, onNotify) {                //把回调收集起来，如果states不是等待就马上出发                var defer = new Deferred();                this._callbacks.push(new Callback(defer, onFulfilled, onRejected, onNotify));                if (this.states !== "pending") {                    var data = (this.states === "fulfilled") ? this.value : this.reason;                    this._processCallback(data);                }                return defer.promise;            },            "catch": function (onRejected) {                return this.then(null, onRejected);            },            'finally': function (cleanup) {                                return this.then(cleanup, cleanup);            },            _processCallback: function (data, is_keepCallback) {                //这里的data不接受promise,偷懒没做。哈哈                var promise = this;                if (this.states === "pending") return;                             var states = ("on-" + this.states).toCamelCase();                var promiseCallbacks = this._callbacks;                var length = promiseCallbacks.length;                for (var i = 0, l = promiseCallbacks.length; i < l; i++) {                                      var callback = (is_keepCallback) ?  promiseCallbacks[i] : promiseCallbacks.shift();                    var defer = callback.defer;                                       if (G.isFunction(callback[states])) {                        //要做错误处理哦                        try {                            //调用回调，                            var returnValue = callback[states](data);                            //如果是promise那就乾坤大挪移把promise连连接过去                            if (returnValue instanceof Promise) {                                                              returnValue.then(defer.resolve.bind(defer), defer.reject.bind(defer));//这里要用bind,因为resolve内需要引用this                            }                            else {                                //不是的话就到值传给下一个promise咯                                defer.resolve(returnValue);                            }                                                   }                        catch (e) {                            defer.reject(e);                        }                    }                    else {                        //data不是函数就直接传下去                        defer.resolve(data);                    }                }            },            constructor: Promise        }