Handy TS/JS functions

scratchpad.ts

// Group elements in `xyz` array in `groupSize`-length arrays
const xyz = ['a','b','c','d','e','f','g','h','i'];
const groupSize = 3;

xyz.reduce<string[][]>((result, item, idx) =>
  new Boolean((idx % groupSize
    ? result[result.length-1].push(item)
    : result.push([item])))
  && result,
  []);
// > [ [ 'a', 'b', 'c' ], [ 'd', 'e', 'f' ], [ 'g', 'h', 'i' ] ]