if (document.images) {
  var homeoff = new Image();
  homeoff.src = "images/navigation/home_off.png";
  var homeon = new Image();
  homeon.src = "images/navigation/home_on.png"; 
  
  var dienstenoff = new Image();
  dienstenoff.src = "images/navigation/diensten_off.png";
  var dienstenon = new Image();
  dienstenon.src = "images/navigation/diensten_on.png"; 
  
  var portfoliooff = new Image();
  portfoliooff.src = "images/navigation/portfolio_off.png";
  var portfolioon = new Image();
  portfolioon.src = "images/navigation/portfolio_on.png"; 
  
  var profieloff = new Image();
  profieloff.src = "images/navigation/profiel_off.png";
  var profielon = new Image();
  profielon.src = "images/navigation/profiel_on.png"; 
  
  var contactoff = new Image();
  contactoff.src = "images/navigation/contact_off.png";
  var contacton = new Image();
  contacton.src = "images/navigation/contact_on.png"; 
}

function actMenuItem(imgName) {
  act(imgName);
}

function inactMenuItem(imgName) {
  inact(imgName);
}

function act(imgName) {
  if (document.images)
    document.images[imgName].src = eval(imgName + "on.src");
}

function inact(imgName) {
  if (document.images)
    document.images[imgName].src = eval(imgName + "off.src");
}