jQuery Rollover for If there are any strings after the extension of image

_rollover.js

/*
 Usage:

 HTML
 <img class="js-rollover">

 JS
 require jQuery
 http://jquery.com/download/
 
 $(function(){
   new Rollover().load();
 });

*/

function Rollover(){
  this.target = $('.js-rollover');
  this.regExp = /^(.+_).\.(png|jpe?g|gif)|;\D+\W\w+\.\w+/i;
}

Rollover.prototype.load = function() {
  var self = this;
  self.target.on('mouseenter mouseleave touchstart touchend', $.proxy(self.event, self));
};
Rollover.prototype.event = function(e){
  var self = this;
  switch (e.type) {
    case 'mouseenter':
      self.enter(e.currentTarget);
      break;
    case 'mouseleave':
      self.leave(e.currentTarget);
      break;
    case 'touchstart':
      self.enter(e.currentTarget);
      break;
    case 'touchend':
      self.leave(e.currentTarget);
      break;
  }
};
Rollover.prototype.enter = function(target) {
  var self = this;
  $(target).attr('src', $(target).attr('src').replace(self.regExp, '$1o.$2'));
};
Rollover.prototype.leave = function(target) {
  var self = this;
  $(target).attr('src', $(target).attr('src').replace(self.regExp, '$1n.$2'));
};