解构赋值

1、左右两边结构必须一样（数据类型、个数）

2、右边必须是个东西（语法无误）

3、声明和赋值不能分开（必须在一句话里完成）

javascript">    let arr = [1,2,3]
    let a = arr[0]
    let b = arr[1]
    let c = arr[2]
    console.log(a,b,c) //1,2,3

 解构赋值

javascript">     let [a,b,c] = [1,3,5]
     console.log(a,b,c) //1，3，5

实例1、左右两边结构必须一样

javascript">    let [a,b,c] = [1,3,5,7]
    console.log(a,b,c) //Identifier 'a' has already been declared 标识符a已经被声明

javascript">    let [a,b] = {a:10,b:20}
    console.log(a,b) //{(intermediate value)(intermediate value)} is not iterable 不可迭代

实例2、复杂结构

javascript">    let [arr, json, num, str] = [[1,2,3], {a:10, b:20, c:30}, 66, 'wenmeichao']
    console.log(arr, json, num, str) //Array(3) Object 66 "wenmeichao"

实例3、声明和赋值不能分开

javascript">    let [a,b]
    [a,b] = [1,2] //Missing initializer in destructuring declaration 解构声明缺少初始化
    console.log(a,b)