javascript继承

1、原型赋值继承：直接将父类的一个实例赋给子类的原型，相当于将父类原型上的方法和属性以及挂在this上的方法和属性全部赋给了子类的原型。

function Person(name){
     this.name=name;
     this.className="person" 
}
Person.prototype.getClassName=function(){
     console.log(this.className)
}

function Man(){
}
Man.prototype = new Person();
var man = new Man('aa');  //传入的参数没被接收
console.log(man.name); // undefined
console.log(man.className); //person
console.log(man.getClassName()); //person
console.log(man instanceof Person) //true
console.log(man.constructor) // function Person(name){}

缺点：子类无法通过父类创建私有属性。

2、构造函数继承：只能继承父类构造函数中的实例属性，无法继承父类原型的属性和方法。

function Person(name){
     this.name=name;
     this.className="person";
}
Person.prototype.getClassName=function(){
     console.log(this.className);
}

function Man(name){
  Person.apply(this,arguments);
}
var man = new Man('justin'); 
console.log(man.name); // justin
console.log(man.className); //person
console.log(man.getClassName()); //报错
console.log(man instanceof Person); //false
console.log(man instanceof Man); //true
console.log(man.constructor); // function Man(name){}

3、组合继承：

function Person(name){
     this.name=name || 'default name';
     this.className="person"; 
}
Person.prototype.getClassName=function(){
     console.log(this.className);
}

function Man(name){
  Person.apply(this,arguments);
}
Man.prototype = new Person();

var man = new Man('justin');  
console.log(man.name); // justin
console.log(man.className); //person
console.log(man.getClassName()); //person
console.log(man instanceof Person); //true
console.log(man instanceof Man); //true
console.log(man.constructor); // function Person(name){}
console.log(Man.prototype); // Person{name: "default name", className: "person"} 原型中的name属性还是存在

4、寄生组合继承（实用）：构造函数属性继承，父类原型继承。

function Person(name){
     this.name=name;
     this.className="person" ;
}
Person.prototype.getClassName=function(){
     console.log(this.className);
}

function Man(name){
  Person.apply(this,arguments);
}
Man.prototype = Object.create(Person.prototype);
Man.prototype.constructor = Man;

var man = new Man('justin');  
console.log(man.name); // justin
console.log(man.className); //person
console.log(man.getClassName()); //person
console.log(man instanceof Person); //true
console.log(man instanceof Man); //true
console.log(man.constructor); // function Man(name){}
console.log(Man.prototype); // Person{}