function getWindowHeight() {
     var windowHeight = 0;
     if (typeof(window.innerHeight) == 'number') {
          windowHeight = window.innerHeight;
     }
     else {
          if (document.documentElement && document.documentElement.clientHeight) {
               windowHeight = document.documentElement.clientHeight;
          }
          else {
               if (document.body && document.body.clientHeight) {
                    windowHeight = document.body.clientHeight;
               }
          }
     }
     return windowHeight;
}