getViewportDimensions.js

function viewport()
{
var e = window
, a = 'inner';
if ( !( 'innerWidth' in window ) )
{
a = 'client';
e = document.documentElement || document.body;
}
return { width : e[ a+'Width' ] , height : e[ a+'Height' ] }
}

/*
USAGE:

var width = viewport().width
var height = viewport().height
*/