js继承的四种方式！

通过原型继承！

为了数据共享,改变原型指向,做到了继承---通过改变原型指向实现的继承
缺陷:因为改变原型指向的同时实现继承,直接初始化了属性，继承过来的属性的值都是一样的了,所以,这就是问题
只能重新调用对象的属性进行重新赋值,

       function Person(name,age,sex,weight) {
         this.name=name;
         this.age=age;
         this.sex=sex;
         this.weight=weight;
       }
       Person.prototype.sayHi=function () {
         console.log("您好");
       };
       function Student(score) {
         this.score=score;
       }
       //希望人的类别中的数据可以共享给学生---继承
       Student.prototype=new Person("小明",10,"男","50kg");
    
       var stu1=new Student("100");
       console.log(stu1.name,stu1.age,stu1.sex,stu1.weight,stu1.score);
       stu1.sayHi();
    
       var stu2=new Student("120");
       stu2.name="张三";
       stu2.age=20;
       stu2.sex="女";
       console.log(stu2.name,stu2.age,stu2.sex,stu2.weight,stu2.score);
       stu2.sayHi();
       var stu3=new Student("130");
       console.log(stu3.name,stu3.age,stu3.sex,stu3.weight,stu3.score);
       stu3.sayHi();

2、借用构造函数继承
借用构造函数:构造函数名字.call(当前对象,属性,属性,属性....);
解决了属性继承,并且值不重复的问题
缺陷:父级类别中的方法不能继承

    function Person(name, age, sex, weight) {
      this.name = name;
      this.age = age;
      this.sex = sex;
      this.weight = weight;
    }
    Person.prototype.sayHi = function () {
      console.log("您好");
    };
    function Student(name,age,sex,weight,score) {
      //借用构造函数
      Person.call(this,name,age,sex,weight);
      this.score = score;
    }
    var stu1 = new Student("小明",10,"男","10kg","100");
    console.log(stu1.name, stu1.age, stu1.sex, stu1.weight, stu1.score);

    var stu2 = new Student("小红",20,"女","20kg","120");
    console.log(stu2.name, stu2.age, stu2.sex, stu2.weight, stu2.score);

    var stu3 = new Student("小丽",30,"妖","30kg","130");
    console.log(stu3.name, stu3.age, stu3.sex, stu3.weight, stu3.score);

3、组合继承

原型实现继承
借用构造函数实现继承
组合继承:原型继承+借用构造函数继承

    function Person(name,age,sex) {
      this.name=name;
      this.age=age;
      this.sex=sex;
    }
    Person.prototype.sayHi=function () {
      console.log("阿涅哈斯诶呦");
    };
    function Student(name,age,sex,score) {
      //借用构造函数:属性值重复的问题
      Person.call(this,name,age,sex);
      this.score=score;
    }
    //改变原型指向----继承
    Student.prototype=new Person();//不传值
    Student.prototype.eat=function () {
      console.log("吃东西");
    };
    var stu=new Student("小黑",20,"男","100分");
    console.log(stu.name,stu.age,stu.sex,stu.score);
    stu.sayHi();
    stu.eat();
    var stu2=new Student("小黑黑",200,"男人","1010分");
    console.log(stu2.name,stu2.age,stu2.sex,stu2.score);
    stu2.sayHi();
    stu2.eat();

    //属性和方法都被继承了

4、拷贝继承

    //拷贝继承；把一个对象中的属性或者方法直接复制到另一个对象中

    function Person() {
    }
    Person.prototype.age=10;
    Person.prototype.sex="男";
    Person.prototype.height=100;
    Person.prototype.play=function () {
      console.log("玩的好开心");
    };
    var obj2={};
    //Person的构造中有原型prototype,prototype就是一个对象,那么里面,age,sex,height,play都是该对象中的属性或者方法

    for(var key in Person.prototype){
      obj2[key]=Person.prototype[key];
    }
    console.dir(obj2);
    obj2.play();