1. var a = [
  2.     ['a', 'b', 'c'],
  3.     ['e', 'f'],
  4.     ['g', 'h', 'i', 'j'],
  5.     ['k']
  6. ];
  7.  
  8. var f = function (data, i) {
  9.     var result = [],
  10.         tmp,
  11.         j, k,
  12.         variants;
  13.     // start from 0 index of data at function launch if index wasn't passed
  14.     i = i || 0;
  15.     // in case i is greater then array bound, just return empty array
  16.     if (i < data.length) {
  17.         for (j = 0; j < data[i].length; j++) {
  18.             variants = f(data, i + 1);
  19.             // if there aren't variants, just create array of one element which is empty array itself
  20.             if (!variants.length) {
  21.                 variants = [
  22.                     []
  23.                 ];
  24.             }
  25.             for (k = 0; k < variants.length; k++) {
  26.                 // concat variants and current iterable element
  27.                 tmp = [data[i][j]].concat(variants[k]);
  28.                 result.push(tmp);
  29.             }
  30.         }
  31.     }
  32.     return result;
  33. }
  34.  
  35. console.log(f(a));