Position du focus dans un texte area

Code:
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<textarea cols="50" rows="10" onfocus="essai(this);">zgfdjbf
jefbhjbgf
kebfjrebg
</textarea>
 
<script type="text/javascript">
function essai(obj){
	if(obj.setSelectionRange){
		obj.setSelectionRange(0,0);
	}else if(obj.createTextRange){
		var range = obj.createTextRange(); 
		range.collapse(true); 
		range.moveEnd('character', 0); 
		range.moveStart('character', 0); 
		range.select();
	}
}
</script>