function imagerollover(){
var allimages=document.getElementsByTagName("img")
var preloadimages=[]
for (var i=0; i<allimages.length; i++){
if (allimages[i].getAttribute("data-over")){ //if image carries "data-over" attribute
preloadimages.push(new Image()) //preload "over" image
preloadimages[preloadimages.length-1].src=allimages[i].getAttribute("data-over")
allimages[i].onmouseover=function(){
this.src=this.getAttribute("data-over")
}
allimages[i].onmouseout=function(){
this.src=this.getAttribute("data-out")
}}}}
imagerollover()