<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>电灯开关</title>
<script type="text/javascript">
var flag = false;
function run() {
var l = document.getElementById("light")
if(flag) {
l.src = "img/off.gif"
flag = false
} else {
l.src = "img/on.gif"
flag = true
}
}
</script>
</head>
<body>
<img id="light" onclick="run()" src="img/off.gif" />
</body>
</html>