Javascript String nthIndexOf(pattern, n)

/**/*from   ww  w  .ja v a2  s  .  c o  m*/
 * Gets the nth occurrence of a pattern in a string
 * @param pattern  Pattern to search
 * @param n  Nth occurrence
 * @return index of nth occurrence or -1 if not found
 */
String.prototype.nthIndexOf = function(pattern, n) {
 var index = -1;
 while (n-- && index++ < this.length) {
  index = this.indexOf(pattern, index);
  if (index < 0) { break; }
 }
 return index;
}