Adds new items to the start of a list, and returns the new length.
This function generates a change (except when called on a variable).
list.unshift(item1, item2, ..., itemX)
Returns the new length of the list.
This code inserts values to the start of a list:
list = [4, 5, 6];
list.unshift(1, 2, 3); // Returns the new length, 6
list;
Return value in JSON format
[1, 2, 3, 4, 5, 6]