Class - inheritance

Class - inheritance

Inheritance allows subclasses to get the parent class (base class), the property can be expanded, adding new methods and properties, etc.

extends

    class P {
        constructor(name,age) {
            this.name = name
            this.age = age
        }
        say () {
            console.log(this.name)
        }

    }

    class L extends  P {
        constructor(name,age,sex,hobby) {
            super(name,age)
            this.sex = sex
            this.hobby = hobby
        }
        say() {
            console.log(`${this.name} + ${this.hobby}`)
        }
    }


    let p = new P ("xiaoming",32)
    p.say() //xiaoming

    let l = new L("kangkang",23,"man","唱歌")
    l.say() //kangkang + 唱歌

It will be subject to a subclass of a subclass of the parent class and method of the same name.

super()effect

1. As a parent class constructor calls

   After calling subclass you can get the properties and methods of the parent class (to be on call at the beginning) (subclass of this in the constructor of the parent class to run again)

2. Calls as a way to target

   1. Non-static method to access super -> parent class prototype

   2. Access super in a static method -> parent

      When calling super, the parent class operation this is always this subclass

    class L extends  P {
        constructor(name,age,sex,hobby) {
            super(name,age)
            this.sex = sex
            this.hobby = hobby
        }
        say() {
            console.log(`${this.name} + ${this.hobby}`)
        }
    }
    

Polymorphism

The same interface, do different things in different situations (same interfaces, different manifestations)

    class L extends  P {
        constructor(name,age,sex,hobby) {
            super(name,age)
            this.sex = sex
            this.hobby = hobby
        }
        say() {
                super.say() // 同一函数名不同结果
            console.log(`${this.name} + ${this.hobby}`)
        }
    }
    

Overload

Different function parameters, different operations

ES5 class inheritance to achieve

function P() {
        this.name = "kangang"
        this.gender = 2
        this.say = function () {
            console.log("我是父类的哦！")
        }
    }
    P.prototype.test = function() {
        console.log(`我是原型上的test方法！！！`)
    }
    function C() {
        P.call(this)
        this.name = "xiaojun"
        this.age = 21
    }

    var child = new C()
    child.say() //我是父类的哦！
    child.test() // child.test is not a function
    
    // 上面的解决方法是
    C.prototype = new P()