var viewportwidth;
var viewportheight;

// the more standards compliant browsers (mozilla/netscape/opera/IE7) use window.innerWidth and window.innerHeight

if (typeof window.innerWidth != 'undefined') {
  viewportwidth = window.innerWidth,
  viewportheight = window.innerHeight
}

// IE6 in standards compliant mode (i.e. with a valid doctype as the first line in the document)

else if (typeof document.documentElement != 'undefined'
 && typeof document.documentElement.clientWidth !=
 'undefined' && document.documentElement.clientWidth != 0) {
   viewportwidth = document.documentElement.clientWidth,
   viewportheight = document.documentElement.clientHeight
} else { // older versions of IE
   viewportwidth = document.getElementsByTagName('body')[0].clientWidth,
   viewportheight = document.getElementsByTagName('body')[0].clientHeight
}
//document.write('<p>Your viewport width is '+viewportwidth+'x'+viewportheight+'</p>');