面向对象class继承

class Student {
            constructor(name) {
                this.name = name;
            }
            hello(){
                alert("hello");
            }
        }
        var xiaoming = new Student("xiaoming");

 class Student {
            constructor(name) {
                this.name = name;
            }
            hello(){
                alert("hello");
            }
        }

        class XiaoStudengt extends Student{
            constructor(name,grade) {
                super(name);
                this.grade = grade;
            }
            myGrade(){
                alert('我是一名小学生')
            }
        }
        var xiaoming = new Student("xiaoming");

原型链：