Ext.onReady(
  function() {
    Ext.select('img.rollover', true).each(function(i, thiz, index) {
      var os = i.dom.src, ni = document.createElement('img');
      i.on('mouseout', function(e) {i.dom.src = os;});
      ni.src = i.dom.src.replace(/(.*)\.(jpg|gif|png)$/i, "$1-sel.$2");
      i.on('mouseover', function(e) {i.dom.src = ni.src;});
    });
  }
);