Javascript validation on multiline texbox for character count

<script language="javascript">
function validateLimit(obj, divID, maxchar) {

objDiv = get_object(divID);

if (this.id) obj = this;

var remaningChar = maxchar - trimEnter(obj.value).length;

if (objDiv.id) {
objDiv.innerHTML = remaningChar + " characters left";
}
if (remaningChar <= 0) {
obj.value = obj.value.substring(maxchar, 0);
if (objDiv.id) {
objDiv.innerHTML = "0 characters left";
}
return false;
}
else
{ return true; }
}

function get_object(id) {
var object = null;
if (document.layers) {
object = document.layers[id];
} else if (document.all) {
object = document.all[id];
} else if (document.getElementById) {
object = document.getElementById(id);
}
return object;
}
function trimEnter(dataStr) {
return dataStr.replace(/(\r\n|\r|\n)/g, "");
}

</script>


-------------------------
<asp:TextBox ID="txtprojectdesc"
MaxLength="240" CssClass="textbox_reg" TextMode="MultiLine"
Rows="5" Width="200px"

ToolTip="Summary:(240 characters)"

onkeyup="return validateLimit(this, 'lblMsg1',240)"

runat="server">
</asp:TextBox><br />
<div id="lblMsg1" class="messagetip">240 characters left</div>