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; 
}