<script type="text/javascript">

    //模拟Promise，改善resolve原型方法

    var Promise = function () {

        this.thens = [];

    };

    Promise.prototype = {

        constructor: Promise,

        then: function(callback){

            this.thens.push(callback);

            return this;

        },

        resolve: function () {

            var t,p;

            t = this.thens.shift();

            t && (p = t.apply(null, arguments));

            while(t && !(p instanceof Promise)){

                t = this.thens.shift();

                t && (p = t.call(null, p));

            }

            if(this.thens.length){

                p.thens = this.thens;

            };

        }

    }

    function f1() {

        var promise = new Promise();

        setTimeout(function () {

            console.log(1);

            promise.resolve();

        }, 5000)

        return promise;

    }

    function f2() {

        var promise = new Promise();

        setTimeout(function () {

            console.log(2);

            promise.resolve();

        }, 5000);

        return promise;

    }

    function f3() {

        var promise = new Promise();

        setTimeout(function () {

            console.log(3);

            promise.resolve();

        }, 5000)

        return promise;

    }

    function f4() {

        console.log(4);

        return 11;

    }

    function f5(x) {

        console.log(x+1);

    }

    function f6() {

        var promise = new Promise();

        setTimeout(function () {

            console.log(6);

            promise.resolve();

        }, 5000)

        return promise;

    }

    function f7() {

        console.log(7);

    }

    var that = f1().then(f2).then(f3).then(f4).then(f5).then(f6).then(f7);

</script>