Lestat621,
Вариант с остановкой ... кликнуть по надписи.
<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8" />
<title></title>
</head>
<body>
<div style="background-color: red">click</div>
<script>
var interv,id2 ;
id2 = document.getElementsByTagName('div')[0];
function opacity(element, speed){
interv = setInterval(function(){
if(+element.style.opacity>1||!element.style.opacity){
element.style.opacity = 0;
}
element.style.opacity = +element.style.opacity + 0.08;
}, speed)
}
id2.onclick = function(){
clearInterval(interv)
}
opacity(id2, 1000);
</script>
</body>
</html>