• 面向对象之类与实例、类与继承


    一、类与实例:

      1、类的声明:

    /*类的声明*/
    function Animal1(){
         this.name = 'name';
    }
    
    
    /*ES6中 calss 的声明*/
    class  Animal2{
        constructor(){
             this.name = name;
       }
    }

       2、生成实例:

    console.log(new Animal1(),new Animal2());
    
    /*
    *打印结果为
    *
    * Animal1{name: 'name'}
    * Animal2{name: ''}
    *
    */

    二、类与继承:

    实现继承的几种方式:

      1、借助构造函数实现继承(原理是在子类中改变父级this的指向,缺点是只能部分继承,

              不能继承父类原型上的方法);

    function Parent() {
        this.name = "parent";
        this.list = [1, 2]
     }
    Parent.prototype.say = "Hi";
    
    function Son() { 
        Parent.call(this);
        this.type = "12";
     }
     console.log(new Parent(),new Son());
     console.log(new Son().say);    //报错

     2、借助原型链实现继承(缺点是原型链上的对象是共用的,改变某个对象的属性,

       原型链上的其他对象属性也会改变);

    function Parent(){
        this.name = "parent";
        this.play = [1, 23]
    }
    
    function Son() {
        this.age = 23;
    }
    Son.prototype = new Parent(); 
    var s1 = new Son();
    var s2 = new Son();
    s1.play.push(4);
    console.log(new Person1, new Person3)
    console.log(s1.play, s2.play);        //结果相等,都为[1,23,4]

    3、组合方式(缺点是父级的构造函数执行了俩次并把父类的constructor也继承了);

    function Parent() {
        this.name = "parent";
        this.play = [1, 2];
    }
    
    Parent.prototype.say = "hi";
    
    function Son() {
        Parent.call(this);
        this.age = 12;
    }
    Son.prototype = new Parent();
    console.log(new Parent(), new Son());
    var s3 = new Son();
    var s4 = new Son();
    s3.play.push(4);
    console.log(s3.play, s4.play, s3.say); // [1,2,4],[1,2],hi

    4、组合优化1(缺点是把父类的constructor也继承了);

    function Parent1() {
        this.name = "parent";
    }
    
    function Son1() {
        Parent1.call(this);
        this.age = 12;
    }
    Son1.prototype = Parent1.prototype; 
    console.log(new Son1(), new Parent1());
    console.log(new Son1().constructor);  // function Parent1(){this.name = "parent"}

     5、组合优化2(原理是通过 Object.create() 方法创建一个中间对象,参数是该对象的

      原型对象,然后把子类的构造函数赋值为子类);

    function Parent2() {
        this.name = "parent";
        this.play = [1, 2];
    }
    
    function Son2() {
        Parent2.call(this);
        this.age = 12;
    }
    Son2.prototype = Object.create(Parent2.prototype);
    Son2.prototype.constructor = Son2;
    console.log(new Son2);
    console.log(new Son2().constructor);

    推荐这个方法。

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  • 原文地址:https://www.cnblogs.com/yiyi111/p/12381590.html
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