Compute cartesian product in JavaScript (ES6).

cartProd.js

const cartProd = (...lists) => {
  if (lists.length < 2) {
    throw new Error('cartProd: need at least 2 lists as arguments');
  }

  const head = (list) => list[0];
  const tail = (list) => list.slice(1);
  const prepend = (head, tail) => [head, ...tail];
  const push = (list, item) => {
    list = list || [];
    list.push(item);
    return list;
  };

  try {
    return genericCartProd(head, tail, prepend, push, ...lists);
  } catch (err) {
    if (err.message === '--- empty ---') {
      return [];
    }
    throw err;
  }
}

const genericCartProd = (head, tail, prepend, push, ...lists) => {
  const hs = head(lists);
  const ts = tail(lists);

  // Cartesian product is an empty set in case one of the lists is empty.
  if (hs.length === 0) {
    throw new Error('--- empty ---');
  }

  // In case this is the last element, we want to turn
  // [a, b, c] into [[a], [b], [c]] and end recursion.
  if (ts.length === 0) {
    return hs.map((x) => [x]);
  }

  // Get CP for tail.
  const cps = genericCartProd(head, tail, prepend, push, ...ts);

  // Prepend items from head to CP for tail.
  var acc;
  for (let hi of hs) {
    for (let pi of cps) {
      acc = push(acc, prepend(hi, pi));
    }   
  }
  return acc;
}

console.log(cartProd([1, 2], [3, 4], [5, 6]));
/*
[ [ 1, 3, 5 ],
  [ 1, 3, 6 ],
  [ 1, 4, 5 ],
  [ 1, 4, 6 ],
  [ 2, 3, 5 ],
  [ 2, 3, 6 ],
  [ 2, 4, 5 ],
  [ 2, 4, 6 ] ]
*/

console.log(cartProd([1, 2], [3, 4], [5, 6], []));
/*
[]
*/