[Dim@]

<div id='div'>lol</div>
<script type='text/javascript'>
Object.prototype.hide = function (){
 var prot = this + '';
 if (/\w?\ HTML\w?/img.test(prot) == true) this.style.display = 'none';
 else if (console) console.log("Ошибка");
};
setTimeout(function(){document.getElementById('div').hide();}, 3000)
</script>