原型，原型链，继承

原型定义

prototype

原型是function对象的一个属性，它定义了构造函数制造出的对象的公共祖先。通过该构造函数产的对象，可以继承原型的属性和方法。原型也是对象。

Person.prototype.LastName = "123";   //祖先
function Person(){
    
}

var person = new Person();
var person1 = new Person();

console.log(person.LastName)
console.log(person1.LastName)
>>>
123
123

更改父类属性

Person.prototype.LastName = "123";
function Person(){
    this.LastName = '32131';
}

var person = new Person();
var person1 = new Person();

console.log(person.LastName)
console.log(person1.LastName)
>>>
32131
32131

继承

1.原型链继承

Grand.prototype.lastName = 'Ji'
function Grand(){


}

var grand = new Grand();

function Father(){
    this.name = 'hehe';
}

var father = new Father();

Son.prototype = father;

function Son(){

}
var son = new Son();

过多的继承了没用的属性。
2.借用构造函数继承

function Person(name,age,sex){
    this.name = name;
    this.age = age;
    this.sex = sex;
}

function Student(name,age,sex,grade){
    Person.call(this,name,age,sex);
    this.grade = grade;
}

var student = new Student();

不能继承借用构造函数的原型；
每次构造函数都要多走一个函数；
3.共享原型

Father.prototype.lastName = 'Deng';
function Father(){
    
}

function Son(){

}
Son.prototype = Father.prototype;

var son = new Son();

改写封装成一个函数

Father.prototype.lastName = 'Deng';
function Father(){
    
}


function Son(){

}
 
function inherit(Target,Origin){ 
    Target.prototype = Origin.prototype
    
}

inherit(Son,Father)
var son = new Son();
var father = new Father();

会影响父类属性

4.圣杯模式

function inherit(Target,Origin){ 
    function F(){};
    F.prototype=Origin.prototype;
    Target.prototype = new F();
    Target.prototype.constructor = Target; //继承的所属
    Target.prototype.uber= Origin.prototype;
}
Father.prototype.lastName = 'Deng';
function Father(){
    
}

function Son(){

}
 

inherit(Son,Father)
var son = new Son();
var father = new Father();