ES6/ES2015核心内容笔记

Var (全局变量，函数变量)

var a = [];
for (let i = 0; i < 10; i++) {
  a[i] = function () {
    console.log(i);
  };
}
a[6](); // 6

Let(块级变量，用来计数的循环变量避免泄露)
const monent = require('moment')
Const(块级常量，值不能改变，引用第三方库时声明的变量)；

class Animal {
    constructor(){
        this.type = 'animal'
    }
    says(say){
        console.log(this.type + ' says ' + say)
    }
}

let animal = new Animal()
animal.says('hello') //animal says hello

class Cat extends Animal {
    constructor(){
        super()
        this.type = 'cat'
    }
}

let cat = new Cat()
cat.says('hello') //cat says hello

Class:定义类
constructor内定义的方法和属性是实例对象自己的，而constructor外定义的方法和属性则是所有实力对象可以共享的
extends关键字实现继承
Super:指代父类的this对象；子类必须在constructor方法中调用super方法，否则新建实例时会报错。因为子类没有自己的this对象，而是继承父类的this对象，然后对其进行加工

function(i){ return i + 1; } //ES5
(i) => i + 1 //ES6
function(x, y) { 
    x++;
    y--;
    return x + y;
}
(x, y) => {x++; y--; return x+y}

解决this的指向问题；

class Animal {
    constructor(){
        this.type = 'animal'
    }
    says(say){
        setTimeout( () => {
            console.log(this.type + ' says ' + say)
        }, 1000)
    }
}
 var animal = new Animal()
 animal.says('hi')  //animal says hi

当我们使用箭头函数时，函数体内的this对象，就是定义时所在的对象，而不是使用时所在的对象。

$("#result").append(`
  There are ${basket.count} items
   in your basket, ${basket.onSale}
  are on sale!
`);

用反引号（`）来标识起始，用${}来引用变量！

解构：

let cat = 'ken'
let dog = 'lili'
let zoo = {cat, dog}
console.log(zoo)  //Object {cat: "ken", dog: "lili"}

let dog = {type: 'animal', many: 2}
let { type, many} = dog
console.log(type, many)   //animal 2

default, rest

function animal(type = 'cat'){
    console.log(type)
}
animal()

function animals(...types){
    console.log(types)
}
animals('cat', 'dog', 'fish') //["cat", "dog", "fish"]