ES6系列笔记-面向对象/继承

王小婷

发布于 2019-12-24 15:34:06

3160

发布于 2019-12-24 15:34:06

一：面向对象

一般面向对象的写法

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title></title>
    </head>
    <body>
    </body>
    <script>
        //一般面向对象的写法
        function User(name, pass) {
            this.name = name;
            this.pass = pass;
        }
        User.prototype.showName = function() {
            console.log(this.name);
        }
        User.prototype.showPass = function() {
            console.log(this.pass);
        }
        var a = new User("wangting", "123456");
        a.showName();
        a.showPass();
    </script>
</html>

存在问题： User既是构造函数，又是类，傻傻分不清打印结果

ES6面向对象写法好处： 1：class关键字，构造器 constructor和类User分开写 2：class里面直接写方法，方法不需要再外挂出去了

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title></title>
    </head>
    <body>
    </body>
    <script>
        //ES6面向对象写法
        class User {
            constructor(name, pass) {
                this.name = name;
                this.pass = pass;
            }
            showName() {
                console.log(this.name);
            }
            showPass() {
                console.log(this.pass);
            }
        }
        var a = new User("wangting", "123456");
        a.showName();
        a.showPass();
      
    </script>
</html>

打印结果

二：继承

继承一个已有类，扩展它的功能一般的继承的写法（es5继承方法），这是在日常开发中经常能看到的写法。

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title></title>
    </head>
    <body>
    </body>
    <script>
        //一般写法
        function User(name, pass) {
            this.name = name;
            this.pass = pass;
        }
        User.prototype.showName = function() {
            console.log(this.name);
        }
        User.prototype.showPass = function() {
            console.log(this.pass);
        }

        //继承方法
        function Children(name, pass, level) {
            User.call(this, name, pass);
            this.level = level;
        }
        //方法
        Children.prototype = new User();
        Children.prototype.constructor = Children;
        Children.prototype.showLevel = function() {
            console.log(this.level)
        }
        var a = new Children("wangxiaoting", "123", 3);
        a.showName();
        a.showPass();
        a.showLevel();
    </script>
</html>

打印结果：

ES6的继承：

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title></title>
    </head>
    <body>
    </body>
    <script>
        //ES6面向对象写法
        class User {
            constructor(name, pass) {
                this.name = name;
                this.pass = pass;
            }
            showName() {
                console.log(this.name);
            }
            showPass() {
                console.log(this.pass);
            }
        }
        //es6的继承(重点)
        class Children extends User {
            constructor(name, pass, level) {
                //继承父级属性
                //同时执行父类的构造函数
                super(name, pass);
                //继续写自己这一层该有的属性
                this.level = level;
            }
            //关于方法，就不需要像旧版new出来xx给.prototype了，因为 extends已经扩展完成了
            //直接写就行
            showLevel() {
                console.log(this.level);
            }
        }
        let c = new Children('wangxiaoting', '123', 23);
        c.showName();
        c.showPass();
        c.showLevel();
    </script>
</html>

打印结果：