https://www.saf.or.jp/en/js/rollover.js

1function smartRollover() {
2	if(document.getElementsByTagName) {
3		var images = document.getElementsByTagName("img");
4		for(var i=0; i < images.length; i++) {
5			if(images[i].getAttribute("src").match("_off."))
6			{
7				images[i].onmouseover = function() {
8					this.setAttribute("src", this.getAttribute("src").replace("_off.", "_on."));
9				}
10				images[i].onmouseout = function() {
11					this.setAttribute("src", this.getAttribute("src").replace("_on.", "_off."));
12				}
13			}
14		}
15	}
16}
17if(window.addEventListener) {
18	window.addEventListener("load", smartRollover, false);
19}
20else if(window.attachEvent) {
21	window.attachEvent("onload", smartRollover);
22}