super關(guān)鍵字用于訪問(wèn)和調(diào)用一個(gè)父對(duì)象上的函數(shù)。
在構(gòu)造函數(shù)中使用時(shí)，super必須放在this之前，否則，會(huì)報(bào)錯(cuò)。

1.在類中使用super

class Polygon {
    constructor(height, width) {
        this.name = 'Polygon';
        this.height = height;
        this.width = width;
    }
    sayName() {
        console.log('Hi, I am a ', this.name + '.');
    }
}

class Square extends Polygon {
    constructor(length) {
        //this.height;  //this不允許使用在super前
        super(length, length);
        this.name = 'Square';
    }

    get area() {
        return this.height * this.width;
    }

    set area(value) {
        //this.area = value;
        console.log(value);
    }
}

var res = new Square(2);
console.log(res,res.area); //Square { name: 'Square', height: 2, width: 2 } 4
res.sayName(); //Hi, I am a  Square.

2. 調(diào)用父類的靜態(tài)方法

class Human {
    constructor() {}
    static ping() {
        return 'ping';
    }
}

class Computer extends Human {
    constructor() {}
    static pingpong() {
        return super.ping() + ' pong';
    }
}
console.log(Computer.pingpong());  //ping pong

3.不能使用delete操作符刪除super上的屬性

class Base {
constructor() {}
foo() {}
}
class Derived extends Base {
constructor() {}
delete() {
 delete super.foo;
}
}

new Derived().delete(); 
// ReferenceError: invalid delete involving 'super'.

4.當(dāng)使用 Object.defineProperty 定義一個(gè)屬性為不可寫時(shí)，super將不能重寫這個(gè)屬性的值。