=transpose(split(join("", arrayformula(rept(filter(A1:A, len(A1:A))&char(9999), counta(B1:B)))), char(9999)))

=transpose(split(rept(join(char(9999), filter(B1:B, len(B1:B)))&char(9999), counta(A1:A)), char(9999)))

a b c 1 2

a 1
a 2
a 3
b 1
b 2
b 3

function crossJoin(arr1, arr2, delim) {

  delim = delim || '';

  var result = [];
  var row = [];
  for (var i = 0; i < arr1.length; i++) {
    for (var j = 0; j < arr2.length; j++) {
      row = [];
      row.push('' + arr1[0,i] + delim + arr2[0,j]);
      result.push(row);
    }
  }
  return result;
}