Array header add element

Add the element item at the beginning of the array arr. Do not directly modify the array arr, the result returns a new array
Input Example:
Prepend ([1, 2, 3, 4], 10)

Output Example:
[10, 1, 2, 3, 4]

function prepend (arr, item) {    return [Item].concat (arr);}

　　

function prepend (arr, item) {     //To copy arr array to a     var a = arr.slice (0);     Use the Unshift method to add Item     a.unshift (item) to the beginning of A;     return A; }

　　

Array header add element