Javascript function to return current viewport height and width (Source: Andy Langton, http://andylangton.co.uk/blog/development/get-viewport-size-width-and-height-javascript)

get-viewport.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' ] };
}