split Arrays into chunks with Javascript

split.js

const split = (arr, fn) => arr.reduce(([first, ...rest],el) =>
    fn(el)
    ? first.length ? [[], first, ...rest] :  [[], ...rest]
    : first.length ? [[...first, el], ...rest] : [[el], ...rest]
    , [[]]).reverse()

const a = [...Array(12).keys()]
split(a, x => !(x%5))
// [ [ 1, 2, 3, 4 ], [ 6, 7, 8, 9 ], [ 11 ] ]