一，instanceof：
instanceof检测左侧的__proto__原型链上，是否存在右侧的prototype原型. 我在之前的两篇文章
[js高手之路]构造函数的基本特性与优缺点
[js高手之路]一步步图解javascript的原型(prototype)对象,原型链
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1 ????????function CreateObj(uName) { 2 ????????????this.userName = uName; 3 ????????????this.showUserName = function () { 4 ????????????????return ‘100‘; 5 ????????????} 6 ????????} 7 ????????CreateObj.prototype.showUserName = function () { 8 ????????????return this.userName; 9 ????????}10 ????????var obj1 = new CreateObj(‘ghostwu‘);11 ????????var obj2 = new CreateObj(‘卫庄‘);12 13 ????????console.log( obj1 instanceof CreateObj ); //true14 ????????console.log( obj2 instanceof CreateObj ); //true15 ????????console.log( obj1 instanceof Object ); //true16 ????????console.log( obj2 instanceof Object ); //true二、isPrototypeOf:
如果隐式原型__proto__指向调用isPrototypeOf()方法的对象原型( CreateObj ), 那么这个方法就返回true，如:
1 ????????var obj1 = new CreateObj(‘ghostwu‘);2 ????????var obj2 = new CreateObj(‘卫庄‘);3 ????????console.log( CreateObj.prototype.isPrototypeOf( obj1 ) ); //true4 ????????console.log( CreateObj.prototype.isPrototypeOf( obj2 ) ); //true
因为obj1,obj2的隐式原型__proto__指向的都是CreateObj.prototype， 有朋友可能会问CreateObj.prototype上面根本就没有isPrototypeOf这个方法，怎么可以
调用呢？
是的，没错，但是CreateObj.prototype的隐式原型__proto__指向了Object.prototype, 而isPrototypeOf存在Object.prototype上，所以就能够调用
三、Object.getPrototypeOf
获取实例的隐式原型(__proto__)的指向，因为obj1,obj2的__proto__都指向CreateObj.prototype
1 ????????var obj1 = new CreateObj(‘ghostwu‘);2 ????????var obj2 = new CreateObj(‘卫庄‘);3 ????????console.log( Object.getPrototypeOf( obj1 ) === CreateObj.prototype ); //true4 ????????console.log( Object.getPrototypeOf( obj2 ) === CreateObj.prototype ); //true
四，实例访问属性和方法时，遵循就近查找原则
实例先在自己身上查找，有，就停止查找，如果没有，就沿着实例的__proto__继续往上查找，有，就停止查找，如果没有就继续沿着原型链一直往上查找，如果
所有的原型对象上都没有，那就是undefined.
1 ????????function CreateObj(uName) { 2 ????????????this.userName = uName; 3 ????????} 4 ????????CreateObj.prototype.showUserName = function () { 5 ????????????return this.userName; 6 ????????} 7 ????????CreateObj.prototype.age = 22; 8 ?9 ????????var obj1 = new CreateObj(‘ghostwu‘);10 ????????obj1.age = 20;11 ????????var obj2 = new CreateObj(‘卫庄‘);12 13 ????????console.log( obj1.age ); //20--->来自实例14 ????????console.log( obj2.age ); //22--->来自原型对象15 16 ????????delete obj1.age;17 ????????console.log( obj1.age ); //22--->来自原型五，hasOwnProperty
判断属性是实例上的还是原型对象上的，如果是实例上的，返回true, 原型上的返回false
1 ????????function CreateObj(uName) { 2 ????????????this.userName = uName; 3 ????????} 4 ????????CreateObj.prototype.showUserName = function () { 5 ????????????return this.userName; 6 ????????} 7 ????????CreateObj.prototype.age = 22; 8 ????????var obj1 = new CreateObj(‘ghostwu‘); 9 ????????obj1.age = 20;10 ????????var obj2 = new CreateObj(‘卫庄‘);11 ????????console.log( obj1.age ); //20--->来自实例12 ????????console.log( obj1.hasOwnProperty( ‘age‘ ) ); //true13 ????????console.log( obj2.age ); //22--->来自原型对象14 ????????console.log( obj2.hasOwnProperty( ‘age‘ ) ); //false15 ????????delete obj1.age;16 ????????console.log( obj1.age ); //22--->来自原型17 ????????console.log( obj1.hasOwnProperty( ‘age‘ ) ); //false六、in操作符
判断属性是否在实例或者原型对象上，只要一个满足条件，返回值都是true
1 ????????function CreateObj(uName) { 2 ????????????this.userName = uName; 3 ????????} 4 ????????CreateObj.prototype.showUserName = function () { 5 ????????????return this.userName; 6 ????????} 7 ????????CreateObj.prototype.age = 22; 8 ????????var obj1 = new CreateObj(‘ghostwu‘); 9 ????????obj1.age = 20;10 ????????console.log( ‘age‘ in obj1 ); //true11 ????????var obj2 = new CreateObj(‘卫庄‘);12 ????????console.log( ‘age‘ in obj2 ); //true13 ????????delete obj1.age;14 ????????console.log( ‘age‘ in obj1 ); //true15 ????????console.log( ‘user‘ in obj1 ); //false16 ????????console.log( ‘user‘ in obj2 ); //false七，结合in和hasOwnProperty的用法，可以封装一个函数判断这个属性是否在原型对象上, 返回值为true:在原型对象上, false:不在原型对象上
1 ????????function CreateObj(uName) { 2 ????????????this.userName = uName; 3 ????????} 4 ????????CreateObj.prototype.showUserName = function () { 5 ????????????return this.userName; 6 ????????} 7 ????????CreateObj.prototype.age = 20; 8 ????????function hasPrototypeProperty( obj, name ){ 9 ????????????return !obj.hasOwnProperty( name ) && ( name in obj );10 ????????}11 ????????var obj1 = new CreateObj(‘ghostwu‘);12 ????????var obj2 = new CreateObj(‘卫庄‘);13 ????????obj1.age = 10;14 ????????console.log( hasPrototypeProperty( obj1, ‘age‘ ) ); //false15 ????????console.log( hasPrototypeProperty( obj2, ‘age‘ ) ); //true八、for...in 可以枚举实例和原型对象上的属性和方法，前提是：该属性和方法是可以枚举的
1 ?????????function CreateObj(uName) { 2 ????????????this.userName = uName; 3 ????????} 4 ????????CreateObj.prototype.showUserName = function () { 5 ????????????return this.userName; 6 ????????} 7 ????????CreateObj.prototype.age = 20; 8 ????????var obj = new CreateObj( ‘ghostwu‘ ); 9 10 ????????for( var key in obj ){11 ????????????console.log( key ); //userName,age,showUserName12 ????????}13 ????????console.log( Object.prototype );14 ????????for( var key in Object.prototype ){15 ????????????console.log( key );//枚举不了, Object.prototype上的属性和方法默认不可枚举,枚举属性为false16 ????????}[js高手之路]原型对象(prototype)与原型链相关属性与方法详解
原文地址：http://www.cnblogs.com/ghostwu/p/7435562.html