类库源码

var Promise = function () {        this.thens = [];    };    Promise.prototype = {        resolve: function () {            var t = this.thens.shift(), n;            t && (n = t.apply(null, arguments), n instanceof Promise && (n.thens = this.thens));        },        then: function (n) {            return this.thens.push(n), this;        }    }

使用方式

function f1() {            var promise = new Promise();            setTimeout(function () {                               alert(1);                promise.resolve();            }, 1500)            return promise;        }        function f2() {            var promise = new Promise();            setTimeout(function () {                alert(2);                promise.resolve();            }, 1500)            return promise;        }        function f3() {            var promise = new Promise();            setTimeout(function () {                alert(3);                promise.resolve();            }, 1500)            return promise;        }        function f4() {                alert(4);        }              f1().then(f2).then(f3).then(f4)

类库思路

主要的思路就是将主Promise下的任务列表(thens)挂靠到子Promise下。当然该库可以封装至ajax、domready等耗时的场景当中，使其可以”thenable"，如：

$$.ajax("assets/xxx.php", {                     method: "GET",                     data: "q=1&rand=" + Math.random()                 }).then(function (msg) {                     alert(msg.responseText)                 });

have fun! =  =!