类与继承，面向对象

类：

<script>
        class Person{
            constructor(){ //构造器
                //this 必须在构造器里面使用
                this.age = 20 //类的属性
                this.sayHello = function(){ //类的方法
                    console.log('hello');
                }
            }
        }  
        //构建对象
        var person = new Person() //无参构造
        console.log(person);//person {age: 20, sayHello: ƒ}
        console.log(person.age); //20
        person.sayHello() //hello
        //调用有参构造
        //类名首字母必须大写 class不能被重复定义
        class Person1{
            // constructor 调用 new 的过程，每一次new里面的内容都会重新声明
            constructor (age = 18,name='jack'){ //构造器
                //this必须在构造器里面使用 this指向实例化的对象
                this.age = age //类的属性
                this.name  = name 
                this.sayHello =function(){ //类的方法
                    console.log('hello');
                }
            }
            run(){ //在函数里面可以访问对应的this
                console.log(this.name + '跑');
            }
        }
        //使用new 调用的对应构造器的时候 就是在实例化的过程 而产生的对象被称为实例化对象
        var person = new Person1(18,'jack')
        console.log(person); //Person1 {age: 18, name: 'jack', sayHello: ƒ}
        var person1 = new Person1(18,'jack')
        console.log(person1); //Person1 {age: 18, name: 'jack', sayHello: ƒ}
        person1.run() //jack跑
        console.log(person1.sayHello == person.sayHello); //flase
        console.log(person1.run == person.run);//true
    </script>

继承：

<script>
       class Father{
           constructor(){
               this.age = 18;
           }
           run(){
               console.log('跑');
           }
       }
       //extends 关键词声明以后 在对应的constructor里面想要使用this 必须先写super()
       class Son extends Father{
           constructor(){
               super() //指向父类Person的构造器constructor
               this.name = 'jack'
           }
       }
       var son = new Son()
       console.log(son); //获取不到run

构建对象的方式

<script>
        class Person{
            constructor(age){//构造器，其实就是一个构造函数
                this.age =age ;
            }
        }
        //new 关键词来构建
        var person = new Person(18)
        console.log(person); //Person {age: 18}
        //使用new关键词来构建
        function   Person1(age){
            this.age =age;
        }
        //new 关键词来构建
        var person = new Person1(20)
        console.log(person); //Person1 {age: 20}
        //当前这个 类型是否是object
        console.log(person instanceof Person1); //true
        //使用工厂模式来构建对象
        function factory(age){
            //声明一个对象
            var obj = new Object()
            //给对象加属性
            obj.age = age 
            //返回这个对象
            return obj;         
        }
        var person1 = factory(23)
        console.log(person1); //{age: 23}
        //当前这个类的类型是否是Person类型
        console.log(person instanceof Person);  //false
    </script>