Underscore.js implementation of Cartesian Product (without any mutable variable). @see: http://stackoverflow.com/questions/12303989/cartesian-product-of-multiple-arrays-in-javascript

cartesian-product.js

function cartesianProductOf() {
    return _.reduce(arguments, function(a, b) {
        return _.flatten(_.map(a, function(x) {
            return _.map(b, function(y) {
                return x.concat([y]);
            });
        }), true);
    }, [ [] ]);
};

cartesianProductOf([1, 2], [3, 4], ['a', 'b'])); // [[1,3,"a"],[1,3,"b"],[1,4,"a"],[1,4,"b"],[2,3,"a"],[2,3,"b"],[2,4,"a"],[2,4,"b"]] 

function cartesianProduct(var_sets) {
  const args = [].slice.call(arguments, 0);

  return args.reduce((a, b)=> (
    _.flatten(
      a.map(x => b.map(y => x.concat([y]))))
    )
  , [[]]);
}

You don't need to use arguments, slice, or call, if you use a rest parameter:

const xProd = (...args) => args.reduce((a, b) => (
    _.flatten(
      a.map(x => b.map(y => x.concat([y]))))
    )
  , [[]]
)