let arr =원본배열.slice()
let tmp = arr.shift()
arr.splice(1,0 , tmp)1 2 3
4 5 6
7 8 9 ->
4 5 6
1 2 3
7 8 9
He threw his knapsack over the brick wall
let arr =원본배열.slice()
let tmp = arr.shift()
arr.splice(1,0 , tmp)1 2 3
4 5 6
7 8 9 ->
4 5 6
1 2 3
7 8 9