前端面试题之JSES5和ES6继承的区别

前端面试题之JSES5和ES6继承的区别

ES5的继承方法可以看这篇：
https://blog.csdn.net/qq593249106/article/details/83098432

ES5与ES6的继承方法对照：
ES5

function Parent() {
    this.name = 'parent';
    this.arr = [1,2,3,4];
}
Parent.prototype.say = function () {
    console.log('say');
};
function Child(age) {
    Parent.call(this);
    this.age = age;
}
Child.prototype = Object.create(Parent.prototype);
Child.prototype.constructor = Child;
var c = new Child(12);
console.log(c.name); //输出parent
c.say(); //输出say
console.log(c.constructor); //输出function Child(age) {Parent.call(this);this.age = age;}
console.log(new Parent().constructor); //输出Parent() {this.name = 'parent';this.arr = [1,2,3,4];}

ES6

class Parent2 {
    constructor() {
        this.name = 'parent';
    }
}
Parent2.prototype.say = function () {
    console.log('say');
};
class Child2 extends Parent {
    constructor(age) {
        super();
        this.age = age;
    }
}
var c2 = new Child2(12);
console.log(c2.name); //输出parent
c2.say(); //输出say
console.log(c.constructor); //输出function Child(age) {Parent.call(this);this.age = age;}
console.log(new Parent().constructor); //输出Parent() {this.name = 'parent';this.arr = [1,2,3,4];}

ES5的继承实质上是先创建子类的实例对象，然后再将父类的方法添加到this上（Parent.apply(this)），然后再把原型链继承。

ES6的继承机制完全不同，实质上是先创建父类的实例对象this（所以必须先调用父类的super()方法，才可使用this关键字，否则报错。），然后再用子类的构造函数修改this实现继承。