function Stack(){}Stack.prototype.push = function (v){    this.head = {        v:v,        next:this.head    };};Stack.prototype.pop = function () {    if(this.head.next !== undefined){        var top = this.head.v;        this.head = this.head.next;        console.log(top);        return top;    }else{        console.log(this.head.v);        return this.head.v;    }};复制代码