Python-like itertools.product function in javascript

product.js

function product() {
  var args = Array.prototype.slice.call(arguments); // makes array from arguments
  return args.reduce(function tl (accumulator, value) {
    var tmp = [];
    accumulator.forEach(function (a0) {
      value.forEach(function (a1) {
        tmp.push(a0.concat(a1));
      });
    });
    return tmp;
  }, [[]]);
}

console.log(product([1], [2, 3], ['a', 'b']));

Generic version for Typescript:

const combinations = <T>(sets: T[][]): T[][] => {
  if (sets.length === 1) {
    return sets[0].map((el) => [el]);
  } else
    return sets[0].flatMap((val) =>
      combinations(sets.slice(1)).map((c): T[] => [val].concat(c))
    );
};