Chunk & flatten

array.ts

export function flatten<T>(array: T[][]): T[] {
  return [].concat.apply([], array);
}

export function chunk<T>(
  array: T[],
  chunkSize: number,
  acc: T[][] = []
): T[][] {
  return array.length > chunkSize
    ? chunk(array.slice(chunkSize), chunkSize, [
        ...acc,
        array.slice(0, chunkSize)
      ])
    : [...acc, array];
}