js原型与原型链

var a = {};
console.log(a.prototype);  //undefined
console.log(a.__proto__);  //Object {}
var b = function(){}
console.log(b.prototype);  //b {}
console.log(b.__proto__);  //function() {}

/*1、字面量方式*/
var a = {};
console.log(a.__proto__);  //Object {}
console.log(a.__proto__ === a.constructor.prototype); //true
/*2、构造器方式*/
var A = function(){};
var a = new A();
console.log(a.__proto__); //A {}
console.log(a.__proto__ === a.constructor.prototype); //true
/*3、Object.create()方式*/
var a1 = {a:1}
var a2 = Object.create(a1);
console.log(a2.__proto__); //Object {a: 1}
console.log(a.__proto__ === a.constructor.prototype); //false（此处即为图1中的例外情况）

var A = function(){};
var a = new A();
console.log(a.__proto__); //A {}（即构造器function A 的原型对象）
console.log(a.__proto__.__proto__); //Object {}（即构造器function Object 的原型对象）
console.log(a.__proto__.__proto__.__proto__); //null