小操作(持续学习，持续更新)

交换位置

function move(arr, from, to) {
    const newA = [...arr] //定义 新数组，不能改变原来的数组
   let item = newA.splice(from, 1) // 取出这个数组
    newA.splice(to, 0, ...item)
    return newA
    }
let a = [1, 2, 3, 4]
    console.log(move(a, 1, 3)) ===>[1,3,4,2]

数组清空

1. 普通清空

let a = [1, 2, 3, 4]
let arr = a
a = []
console.log(a) ==>[]
console.log(arr)  ==>[1,2,3,4]

2. 彻底清空

let a = [1,2,3,4]
let arr = a
a.length = []
console.log(a) ===>[]
console.log(arr) ==>[]