you cannot get the mouse coordinates on the server side unless you submit them back, but it is not recommended, since the mouse-related messages are massive in quantity
try
labe1.innerText = dv2;
but the change will not be reflected on the server side, if you really want the value on the server side, use a hidden input control like
<form runat=server>
<input type=hidden id=hid runat=server>
...
</form>
on the client side in javascript:
document.all("hid").value = dv2;