[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]
[1,2,3,4,9,10,11,12,5,6,7,8,13,14,15,16]
arr = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]; arr.splice(8,0,arr.splice(4,4)); alert(arr)