JavaScript类继承

Posted 2021-10-23 wsyjlly

1. 和其他功能一样，ECMAScript 实现继承的方式不止一种。这是因为 javascript 中的继承机制并不是明确规定的，而是通过模仿实现的。这意味着所有的继承细节并非完全由解释程序处理。作为开发者，你有权决定最适用的继承方式。
2. 创建的子类将继承超类的所有属性和方法，包括构造函数及方法的实现。记住，所有属性和方法都是公用的，因此子类可直接访问这些方法。子类还可添加超类中没有的新属性和方法，也可以覆盖超类的属性和方法。
3. 继承的方式：

• 对象冒充方式方式一

       /*被继承类*/
    function Animal_1(name) {
        this.name = name;
        this.printName = function () {
            console.log(this.name);
        }
    }
    function Person_1(name,age) {
        this.method1 = Animal_1;
        this.method1(name);
        this.age = age;
        this.printAge = function () {
            console.log(this.age);
        }
    }
    var o1 = new Person_1("ysw",18);
    var o2 = new Animal_1("ysw");
    console.log(o1);
    nsole.log(o2);
    console.log(o1 instanceof Animal_1);
    console.log(o1 instanceof Person_1);
    console.log(o2 instanceof Animal_1);
    console.log(o2 instanceof Person_1);

• 对象冒充方式方式二：利用call方法和apply方法

    function Animal_2(name) {
        this.name = name;
        this.printName = function () {
            console.log(this.name);
        }
    }
    function Person_2(name,age) {
        Animal_2.call(this,name);
        // Animal_2.apply(this,new Array(name));
        this.age = age;
        this.printAge = function () {
            console.log(this.age);
        }
    }
    o1 = new Person_2("ysw",18);
    o2 = new Animal_2("ysw");
    console.log(o1);
    console.log(o2);
    console.log(o1 instanceof Animal_2);
    console.log(o1 instanceof Person_2);
    console.log(o2 instanceof Animal_2);
    console.log(o2 instanceof Person_2);

• 原型链方式

        /*被继承类*/
    function Animal_3() {
    }
    Animal_3.prototype.name = "ysw";
    Animal_3.prototype.printName = function () {
        console.log(this.name);
    };
    function Person_3() {
    }
    Person_3.prototype = new Animal_3();
    Person_3.prototype.age = 18;
    Person_3.prototype.printAge = function () {
        console.log(this.age);
    };
    o1 = new Person_3();
    o2 = new Animal_3();
    console.log(o1);
    console.log(o2);
    console.log(o1 instanceof Animal_3);
    console.log(o1 instanceof Person_3);
    console.log(o2 instanceof Animal_3);
    console.log(o2 instanceof Person_3);

• 混合方式

        /*被继承类*/
    function Animal_4(name) {
        this.name = name;
    }
    Animal_4.prototype.printName = function () {
        console.log(this.name);
    };
    function Person_4(name,age) {
        Animal_4.call(this,name);
        this.age = age;
    }
    Person_4.prototype = new Animal_4();
    Person_4.prototype.printAge = function () {
        console.log(this.age);
    };
    o1 = new Person_4("晏沈威",22);
    o2 = new Animal_4("晏沈威");
    console.log(o1);
    console.log(o2);
    console.log(o1 instanceof Animal_4);
    console.log(o1 instanceof Person_4);
    console.log(o2 instanceof Animal_4);
    console.log(o2 instanceof Person_4);

• ES6语法 class extends继承

        /*被继承类*/
    class Animal_5 {
        constructor(name){
            this.name = name;
        }
        printName(){
            console.log(this.name);
        }
    }
    class Person_5 extends Animal_5{
        constructor(name,age){
            super(name);
            this.age = age;
        }
        printAge() {
            console.log(this.age);
        };
    }
    o1 = new Person_5("晏沈威",22);
    o2 = new Animal_5("晏沈威");
    console.log(o1);
    console.log(o2);
    console.log(o1 instanceof Animal_5);
    console.log(o1 instanceof Person_5);
    console.log(o2 instanceof Animal_5);
    console.log(o2 instanceof Person_5);