JS原型链怎么理解

  // _proto_
 在函数里有一个属性prototype
 由该函数创建的对象默认会连接到该属性上
   //prototype 与 _proto_ 的关系
 _proto_是站在对象角度来说的
 prototype 是站在构造函数角度来说的

var obj = new Object();
对象是有原型对象的
原型对象也有原型对象 
  obj._proto_._proto_._proto_
原型对象也有原型对象，对象的原型对象一直往上找，会找到一个null
// 原型链示例
  var arr = [];
  arr -> Array.prototype ->Object.prototype -> null
  var o = new Object();
  o -> Object.prototype -> null;
  function Foo1(){
  this.name1 = '1';
}
function Foo2(){
  this.name2 = '2';
}
Foo2.prototype = new Foo1();
function Foo3(){
  this.name = '3';
}
Foo3.prototype = new Foo2();
var foo3 = new Foo3();
console.dir(foo3);

function Animal(name){
    this.name = name;
  }
  function Tiger(color){
    this.color = color;
  }
//  var tiger = new Tiger('yellow');
//  console.log(tiger.color);
//  console.log(tiger.name); //undefined
//   Tiger.prototype = new Animal('老虎');  //一种方式
  Object.prototype.name = '大老虎';  //第二种方式
    var tiger = new Tiger('yellow');
    console.log(tiger.color);
    console.log(tiger.name);

————做兼容
 //shim垫片
  function create(obj){
    if(Object.create){
      return Object.create(obj);
    }else{
      function Foo(){}
      Foo.prototype = obj;
      return new Foo();
    }
  }

var obj = {};
 obj.extend = function(obj){
   for(var k in obj){
    this[k] = obj[k];
   }
 }

function Animal(name){
  this.name = name;
}
function Mouse(nickname){
  Animal.call(this,'老鼠');
  this.nickname = nickname;
}
var m = new Mouse('杰瑞');
console.log(m.name);
console.log(m.nickname);

function Person(name){
  this.name = name;
}
Person.prototype.showName = function(){
  console.log(this.name);
}
function Student(name,age){
  Person.call(this,name);
  this.age = age;
}
Student.prototype = new Person();
Student.prototype.contructor = Student;
Student.prototype.showAge = function(){
  console.log(this.age);
}
var stu = new Student('张三',12);
stu.showName();
stu.showAge();