修改原型链的两种方式 ：

Person.prototype.name = 20;
p2.__proto__.name = 2;

系统的一些都是通过原型链的继承方式实现的例如：

div标签：
HTMLDivElement.prototype = new HTMLElement();
HTMLDivElement = {}; ->
HTMLElement.prototype = new Element();
HTMLElement = {};->
Element.prototype = new HTMLElement();
Element = {};

interface HTMLElement extends Element
interface Element extends Node
interface Node extends EventTarget
interface EventTarget

    var p2 = {
        name:'haha'
    };
    Person.prototype = p2;
    var p = new Person();

    var p2 = new Person();

    p2.__proto__.name = 2;
    Person.prototype.name  = 20;
    console.log(p.name);