if (document.getElementById) { window.onload = swap };
function swap() {
var numimages=3;
rndimg = new Array("topimage_historie.jpg", "topimage_sprog.jpg", "topimage_litteratur.jpg"); 
x=(Math.floor(Math.random()*numimages));
randomimage=(rndimg[x]);
document.getElementById("forsideImageTop").style.backgroundImage = "url("+ randomimage +")"; 
}