Hello ayi, I see that you wrote:
position:absolute
well, I tested this and if you change that to position:fixed; it works fine, in my code I made a big green div to demonstrate the scrolling, here...

Hers one, it returns the screen resolution(first width, then height):

<script type="text/javascript">
if (screen.width<800)
{
window.location="Mobile page name"
}
else
{...