JavaScript继承

方法一：通过原型实现继承

    //动物的构造函数
    function Animal(name,weight){
        this.name=name;
        this.weight=weight;
    }
    //动物的原型方法
    Animal.prototype.eat = function(){
      console.log("每天都在吃");
    };
    //狗的构造函数
    function Dog(color){
        this.color=color;
    }
    //狗的原型方法
    Dog.prototype = new Animal("哮天犬","30kg");//改变原型指向
    Dog.prototype.bite = function(){
        console.log("汪汪汪~~咬你");
    };
    //哈士奇
    function ErHa(sex){
        this.sex=sex;
    }
    ErHa.prototype = new Dog("白色");//改变原型指向
    ErHa.prototype.playHost = function(){
        console.log("玩的好开心，哈哈……");
    };

    var erHa = new ErHa("雄性");
    console.log(erHa.name,erHa.weight,erHa.color,erHa.sex);
    erHa.eat();
    erHa.bite();
    erHa.playHost();
    console.dir(erHa);

输出结果：

方法二：借用构造函数继承

    function Person(name,age,sex,weight){
        this.name=name;
        this.age=age;
        this.sex=sex;
        this.weight=weight;
    }
    Person.prototype.sayHi = function(){
        console.log("Hello!");
    };
    function Student(name,age,sex,weight,score){
        //借用构造函数
        Person.call(this,name,age,sex,weight);
        this.score=score;
    }

    var student = new Student("Tom",20,"男","60kg",100);
    console.log(student.name,student.age,student.sex,student.weight,student.score);
    console.dir(student);
    //父类中的方法不能继承，调用会报错：Uncaught TypeError: student.sayHi is not a function
    //student.sayHi();

方法三、组合继承：原型继承+借用构造函数继承

    function Person(name,age,sex,weight){
        this.name=name;
        this.age=age;
        this.sex=sex;
        this.weight=weight;
    }
    Person.prototype.sayHi = function(){
        console.log("Hello!");
    };
    function Student(name,age,sex,weight,score){
        //借用构造函数——继承属性值
        Person.call(this,name,age,sex,weight);
        this.score=score;
    }
    //改变原型指向继承，不用赋值
    Student.prototype = new Person();
    Student.prototype.eat = function(){
        console.log("食堂好多好吃的");
    };

    var student = new Student("Tom",20,"男","60kg",100);
    console.log(student.name,student.age,student.sex,student.weight,student.score);
    student.sayHi(); //可以调用父类原型方法
    student.eat();
    console.dir(student);

方法四、拷贝继承

拷贝继承：把一个对象中的属性和方法直接复制到另一个对象中（通过循环遍历赋给另一个对象）

    function Person(){

    }
    Person.prototype.name="Tom";
    Person.prototype.age=20;
    Person.prototype.sex="男";
    Person.prototype.weight="60kg";
    Person.prototype.sayHi = function(){
        console.log("Hello!");
    };

    var student=[];
    for(var key in Person.prototype){
        student[key]=Person.prototype[key];
    }

    console.log(student.name,student.age,student.sex,student.weight);
    student.sayHi(); 
    console.dir(student);

总结：