ES6新增语法

let声明—-let a=123

  let demo = (a) => {
    console.log(a);
 }
  demo(123)
//123

1. 没有变量提升—必须先声明，再使用
2. 不可重复定义—重复声明报错
3. 块级作用域—-如：if(){},for(){},function(){}这样的代码块

箭头函数—-let demo=(x,y)=>{ }

1. 语法改变，从function (){ }——->()=>{ }

2. 如果函数只有一个参数可以省略括号()

   let demo = a => {
   console.log(a);
   }
   demo(123)
   //123

3. 如果函数只有一个参数且执行语句只有一条可省略{ }花括号

   let demo = a => console.log(a);
   demo(123)

4. this指向问题

   1. 旧函数：谁调用this指向谁，而箭头函数是创建时就确定了this指向

      function fun() {
      let demo = () => {
      console.log(this);
      }
      demo()
      }
      let obj2 = {
      user: 111,
      pwd: 222,
      fun: fun
      }
      obj2.fun()
      //{user: 111, pwd: 222, fun: ƒ}
      //this指向fun()，fun的this指向的obj2

      function fun() {
      console.log(this);
      }
      let obj = {
      name: 123,
      sex: 'nv',
      fun: fun
      }
      obj.fun()
      //{name: 123, sex: 'nv', fun: ƒ}
      //this指向obj

      let demo = () => {
      console.log(this);
      }
      let obj = {
      name: 123,
      sex: 'nv',
      demo: demo
      }
      obj.demo()
      //Window {window: Window, self: Window, document: document, name: '', location: Location, …}
      //指向window

   2. 不可通过call( )，apply( )更改this指向

      let demo = () => {
      console.log(this);
      }
      let obj2 = {
      user: 111,
      pwd: 222,
      fun: fun
      }
      demo.call(obj2)
      //指向window

      let demo = () => {
      console.log(this);
      }
      let obj2 = {
      user: 111,
      pwd: 222,
      fun: fun
      }
      demo.apply(obj2)
      //指向window

   3. 1

   4. 2
   5. 3

模板字符串

1. 旧时拼接

   let str1 = 123
   let str2 = str1 + 'xiaoming'
   console.log(str2);
   //123xioaming

2. ES6拼接

   let str1 = 123
   let str2 = `${str1}xioaming`
   console.log(str2);
   //123xioaming

class类——就是一个语法糖

1. 定义

   class stu1{
   constructor(name,sex){
   this.name=name
   this.sex=sex
   this.grade=function () {
     console.log(123) 
   }
   }
   mood(){
   console.log(234) 
   }
   }
   let class1=new stu1('xiaoming','男')

2. 静态属性和静态方法——-该方法不能通过实例调用/

   class stu1 {
   constructor(name, sex) {
     this.name = name
     this.sex = sex
     this.grade = function () {
       console.log(123)
     }
   }
   mood() {
     console.log(234)
   }
   //静态方法
   static getXingGe() {
     console.log('性格')
   }
   //静态属性
   static name='女'
   }
   let class1 = new stu1('xiaoming', '男')
   console.log(class1);
   class1.mood()
   // class1.getXingGe()---//class1.getXingGe is not a function
   stu1.getXingGe()//只能通过类名调用，不能通过实例对象调用

3. class类继承

4. 私有属性和私有方法

1. for…in循环