为什么可用宽度:undefined可用高度:undefined
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>屏幕分辨率的高和宽</title>
</head>
<body>
<script type="text/javascript">
document.write("可用宽度:"+screen.avaiWidth );
document.write("可用高度:"+screen.avaiHeight );
</script>
</body>
</html>