Javascript String numpad()

/**//from   w ww  .ja va2 s  .  c  o m
@Name: String.prototype.numpad
@Author: Paul Visco
@Version: 1.0 11/19/07
@Description: Pads all numbers under 9 with a zero on the left
@Return: String The original number padded to left with zero
@Example:
var myString = 9;

var newString = myString.numpad();
//newString = '09'
*/
String.prototype.numpad = function(){
 return (this<=9) ? '0'+this : this;
};