function show(ev){
    var element = (ev.target||ev.srcElement);
    element.style.backgroundColor = "palegreen";
}
function addAll(){
    var item;
    var checks = document.getElementsByTagName("span");
    for (item of checks){
	if (item.getAttribute("class") == "check"){
	    item.addEventListener("click",show,false);
	}
    }
}
window.onload = addAll;