function windowHeight() {
  if( typeof( window.innerWidth ) == 'number' ) {    
    return window.innerHeight;
  } else if( document.documentElement && ( document.documentElement.clientWidth || document.documentElement.clientHeight ) ) {    
    return document.documentElement.clientHeight;
  } else if( document.body && ( document.body.clientWidth || document.body.clientHeight ) ) {
    return document.body.clientHeight;
  }
}