JS 基础篇(原型和继承)

原型主要是用来存公共属性和方法

function Animal(){

}
var a=new Animal()
a._prop_=Animal.prototype//对象的_prop_指向函数对象的原型
a.constructor=Animal//对象的构造函数指向函数对象
//a即为Animal的实例也为Animal.prototype的实例

原型继承

function Animal(category){
    this.category = 'Animal';
    this.testrr=['松鼠','小狗'];
    this.sleep = function(){
        console.log('我是sleep');
    }
}
Animal.prototype.run= function(){
    console.log('hhhh');
}

function Dog(name){
    this.name=name;
    this.type='dog';
}

Dog.prototype = new Animal();
Dog.prototype.speak = function(){
    console.log('speak');
}
var  p1= new Dog('小白');

console.log(p1)
p1.category = '蔬菜'
p1.testrr.push('小狗');
p1.sleep = function(){
    console.log('我是sleep');
}
console.log(p1)

// 缺点： 
// 1. 想为子类添加新的方式， 必须放在 new Animal()之后
// 2. 无法实现多继承
// 3. 原型链被破坏
// 4 . 无法向父级传参
// 5. 引用类型的属性会被影响

构造继承

function Animal(category){
    this.category = category;
    this.testrr=['老虎','猫'];
    this.sleep = function(){
        console.log('pp');
    }
}
Animal.prototype.run= function(){
    console.log('tttt');
}

function DogA(category,name){
    // dog1
    Animal.call(this,category);
    // Animal.apply(this,[category]);
    this.name=name;
    this.type='dog';
}

var dog1= new DogA('动物','小白');

//缺点
//1：不能继承原型方法

组合继承

 function Animal(category){
    this.category = category;
    this.testrr=['老虎','猫'];
    this.sleep = function(){
        console.log('pp');
    }
}
Animal.prototype.run= function(){
    console.log('tttt');
}

function DogA(category,name){
    // dog1
    Animal.call(this,category);
    // Animal.apply(this,[category]);
    this.name=name;
    this.type='dog';
}

// DogA.prototype = Object.assign({},Animal.prototype);  
DogA.prototype = Object.create(Animal.prototype);  
DogA.prototype.constructor = DogA;
var dog1= new DogA('动物','小白');
Animal.prototype.km = "poo";
Animal.prototype.walk = function(){
    console.log('ppp');
}