if (document.images) {

  image1on = new Image();
  image1on.src = "images/nav/preconstruction-on.jpg";
  
  image2on = new Image();
  image2on.src = "images/nav/construction-on.jpg";

  image3on = new Image();
  image3on.src = "images/nav/property-on.jpg";

  image4on = new Image();
  image4on.src = "images/nav/realestate-on.jpg";

  image5on = new Image();
  image5on.src = "images/nav/owner-on.jpg";
  
  image6on = new Image();
  image6on.src = "images/nav/project-on.jpg";

  image7on = new Image();
  image7on.src = "images/nav/testimonial-on.jpg";

  image8on = new Image();
  image8on.src = "images/nav/contact-on.jpg";

  image1off = new Image();
  image1off.src = "images/nav/preconstruction-off.jpg";
  
  image2off = new Image();
  image2off.src = "images/nav/construction-off.jpg";
  
  image3off = new Image();
  image3off.src = "images/nav/property-off.jpg";
  
  image4off = new Image();
  image4off.src = "images/nav/realestate-off.jpg";
  
  image5off = new Image();
  image5off.src = "images/nav/owner-off.jpg";
  
  image6off = new Image();
  image6off.src = "images/nav/project-off.jpg";
  
  image7off = new Image();
  image7off.src = "images/nav/testimonial-off.jpg";
  
  image8off = new Image();
  image8off.src = "images/nav/contact-off.jpg";
  
}
function turnOn(imageName) {
  if (document.images) {
    document[imageName].src = eval(imageName + "on.src");
  }
}

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