[drodil]

Nice one. Have you tried replacing the for loops with forEach? It might be even more performant.

[Etheryte]

In Javascript, forEach, map, reduce and other similar array methods are considerably slower than a regular for loop. You can see [0] and the linked questions for more technical details.

[0] https://stackoverflow.com/q/22155280/1470607

[sbr464]

Function callbacks are definitely slower. You could probably shave another 10% by changing the array.push() calls to direct assignments: array[array.length] = value. Same with the nested array.map, changing to a for loop.