// array to store original image src's
var menuItems = new Array();

function menuItem (menuItemId, hover) {
  var menuItem = document.getElementById(menuItemId);

  // switch on or off to hover
  if (hover) {
    menuItems.menuItemId = menuItem.src;
    var menuItemHover = menuItem.src.replace(/(on|off)/, "hover");
    menuItem.src = menuItemHover;
  }
  // return original
  else menuItem.src = menuItems.menuItemId;
}