https://www.trustdent.co.jp/js/rollover_on.js

1// JavaScript Document
2function smartRollover() {
3	if(document.getElementsByTagName) {
4		var images = document.getElementsByTagName("img");
5		for(var i=0; i < images.length; i++) {
6			if(images[i].getAttribute("src").match("_off."))
7			{
8				images[i].onmouseover = function() {
9					this.setAttribute("src", this.getAttribute("src").replace("_off.", "_on."));
10				}
11				images[i].onmouseout = function() {
12					this.setAttribute("src", this.getAttribute("src").replace("_on.", "_off."));
13				}
14			}
15		}
16	}
17}
18if(window.addEventListener) {
19	window.addEventListener("load", smartRollover, false);
20}
21else if(window.attachEvent) {
22	window.attachEvent("onload", smartRollover);
23}