10 sec slideshow (background-image)

document.body.insertAdjacentHTML("beforeend",'<div id="slide1" style="width:100%;height:100%;background-color:#222;background-repeat:no-repeat;background-position:center center;background-size:contain;"></div>');
var a=il.match(/\w+/gim).sort(Math.round(Math.random())-0.5),slide=document.getElementById("slide1"),i=0;
setInterval(function(){slide1.style.backgroundImage="url('http://notebook1.lan/i/"+ a[(i++ % (a.length+1))] + ".jpg')"},10000);
document.body.style.margin="0px";document.body.style.overflowY="hidden";