Splitting into chunks

Paginating results, sending data in batches and laying out items in a three-column grid all come down to the same thing: splitting an array into groups of a fixed size.

The slice method does this without changing the original array: you move forward in steps of size and cut out one piece at each step.

The real test is the edge cases: an empty array, a size that doesn't divide the length evenly, and a size of zero or less. That last one makes the loop run forever if you don't check for it before the loop starts.