product.ts

function is2dArray(arg: any): boolean {
  if (Array.isArray(arg) && arg.length > 0 && arg.every(Array.isArray)) {
    return true;
  } else {
    return false;
  }
}

export function product<T>(array2d: T[][]): T[][] {
  if (!is2dArray(array2d)) {
    throw new RangeError("Invalid argument");
  }
  if (array2d.length === 0) {
    return [[]];
  } else {
    const head: T[] = array2d[0];
    const tail: T[][] = array2d.slice(1);
    const productTail: T[][] = tail.length === 0 ? [[]] : product(tail);
    return head
      .map((ahead) => productTail.map((atail) => [ahead].concat(atail)))
      .flat(1);
  }
}