JS如何实现继承

原型链 利用原型让一个引用类型继承另外一个引用类型的属性和方法

构造函数，原型，实例之间的关系：每个构造函数都有一个原型对象，原型对象包含一个指向构造函数的指针，而实例都包含一个指向原型对象的内部指针。

  function SuperType() {
        this.property = true;
    }
    SuperType.prototype.getSuperValue = function() {
        return this.property;
    }
    function subType() {
        this.property = false;
    }
    //继承了SuperType
    subType.prototype = new SuperType();
    subType.prototype.getSubValue = function (){
        return this.property;
    }
    var instance = new subType();
    console.log(instance.getSuperValue());//true

借用构造函数

在子类型创建的内部调用超类构造函数，通过使用call()和apply()方法可以在新创建的对象上执行构造函数

 function Color() {
        this.colors = ["red","blue","green"];
    }
    function type() {
        Color.call(this);//继承了Color
    }
    var instance1 = new type();
    instance1.colors.push("black");
    console.log(instance1.colors);//"red","blue","green","black"
    var instance2 = new type();
    console.log(instance2.colors);//"red","blue","green"

上面两种技术组合实现继承

function SuperType(name) {
        this.name = name;
        this.colors = ["red","blue","green"];
    }
    SuperType.prototype.sayName = function() {
        console.log(this.name);
    }
    function SubType(name, age) {
        SuperType.call(this,name);//继承属性
        this.age = age;
    }
    //继承方法
    SubType.prototype = new SuperType();
    SubType.prototype.constructor = SubType;
    SubType.prototype.sayAge = function() {
        console.log(this.age);
    }
    var instance1 = new SubType("EvanChen",18);
    instance1.colors.push("black");
    console.log(instance1.colors);//"red","blue","green","black"
    instance1.sayName();//"EvanChen"
    instance1.sayAge();//18
    var instance2 = new SubType("EvanChen666",20);
    console.log(instance2.colors);//"red","blue","green"
    instance2.sayName();//"EvanChen666"
    instance2.sayAge();//20

原型式继承

借助原型可以基于已有的对象创建对象，同时还不必须因此创建自定义的类型

 function object(o) {
        function F(){}
        F.prototype = o;
        return new F();
    }
    var person = {
        name:"TIKME",
        list:["aa","bb","cc"]
    };
    var str = object(person);
    str.list.push("dd");
    var res = object(person);
    res.list.push("ee");
    console.log(person.list);//["aa", "bb", "cc", "dd", "ee"]

寄生式继承

创建一个仅用于封装继承过程的函数，该函数在内部以某种方式来增强对象，最后再像真正是它做了所有工作一样返回对象

function object(o) {
        function F(){}
        F.prototype = o;
        return new F();
    }
    function createAnother(original) {
        var clone = object(original);
        clone.sayHi = function () {
            console.log('hi')
        };
        return clone;
    }
    var person2 = {
        name:"TIKME",
        list:["AA","BB","CC"]
    };
    var anotherPerson = createAnother(person);
    anotherPerson.sayHi();///"hi"
    console.log(person2)