6、扩展运算符（spread）...

扩展运算符

是rest参数的逆运算，将一个数组转为用逗号分隔的参数数列

• 1、孤立数组元素

let iArray = ['1','2','3']
...iArray => 1 ,2,3

• 2、在数组中添加元素

let iArray = ['1','2','3']
let ['0',...iArray,'4'] => ['0','1','2','3','4']

• 3、在数组中删除元素（取出一个元素），与解构赋值结合，只能放在参数最后一位

const [first,...rest] = [1,2,3,4,5]
first --> 1
[...rest] = [2,3,4,5]

• 4、数组的合并

var arr1 = [0,1,2]
var arr2 = [3,4,5]
arr1.push(...arr2) ----> [0,1,2,3,4,5]

推荐使用下面的方法合并数组
var arr1 = [0,1,2]
var arr2 = [3,4,5]
[...arr1,...arr2] ----> [0,1,2,3,4,5]

• 5、字符串转化成数组

let str = "wasgd"
[...str] = ['w','a','s','g','d']

• 6、当做参数传递（和直接传数组的区别）

let arr = ['1','2','3']
hanshu(...arr)
hanshu(...arr){
       console.log(...arr)  ----> 1,2,3
}