if (document.getElementById) { if (window.addEventListener) //DOM method for binding an event
window.addEventListener("load", swap, false)
else if (window.attachEvent) //IE exclusive method for binding an event
window.attachEvent("onload", swap);};
function swap() {
var numimages=4;
rndimg = new Array("/SiteAssets/wrccheader1.jpg", "/SiteAssets/wrccheader2.jpg", "/SiteAssets/wrccheader3.jpg", "/SiteAssets/wrccheader4.jpg"); 
x=(Math.floor(Math.random()*numimages));
randomimage=(rndimg[x]);
document.getElementById("banner").style.backgroundImage = "url("+ randomimage +")"; 
}