比callback更简洁的链式执行promise

promise自己理解的也不够深刻，具体知识点不在这里细说了

直接上个例子，清晰明了，自己去悟吧

<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>