继承

        //es5创建类
        function User(name, pass){
            this.name = name;
            this.pass = pass;
        }

        User.prototype.showName = function(){
            alert(this.name)
        }

        var myUser = new User('Theo', '123');
        
        //es6 创建类
        class User{
            constructor(name, pass){
                this.name = name;
                this.pass = pass;
            }
            
            showName(){
                alert(this.name)
            }
        }

        var myUser = new User('Theo', '123')

        //es5 继承
        function VipUser(name, pass, level){
            User.call(this, name, pass);
            this.level = level;
        }

        VipUser.prototype = new User();
        VipUser.prototype.constructor = VipUser;

        VipUser.prototype.showLevel = function(){
            alert(this.level)
        }

        var vip = new VipUser('Theo', '123', 3);

        //es6 继承
        class VipUser extends User{
            constructor(name, pass, level){
                super(name, pass);
                this.level = level;
            }

            showLevel(){
                alert(this.level)
            }
        }