Add character in between using OnKeyPress event

<script language="javascript" type="text/javascript">

function padCharacter(Cid,ch,num)
{
var elem = document.getElementById(Cid);
var pad = elem.value;
if(!ch) ch="";
if(pad.length == num)
{
pad=pad +ch;
elem.value=pad;

}


}


</script>

txtPlantJob.Attributes.Add("onkeypress", "padCharacter('" + txtPlantJob.ClientID + "','-',2)")