code: function(num, len, radix) {
          var str = num.toString(radix || 10);
          while (str.length < len) {
              str = "0" + str;
          }
          return str;
      }
docs: Method: zeroPad
  Create a zero padded string optionally with a radix for casting numbers.
  
  Parameters:
  num - {Number} The number to be zero padded.
  len - {Number} The length of the string to be returned.
  radix - {Number} An integer between 2 and 36 specifying the base to use
  for representing numeric values.