js如何设置网页横屏和竖屏切换

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="application/xhtml+xml;charset=UTF-8" />
<meta name="viewport" content="width=device-width" />
<title>手机横、竖屏事件</title>
<script language="javascript" type="text/javascript">
//屏幕方向标识，0横屏，其他值竖屏
var orientation=0;
//转屏事件，内部功能可以自定义
function screenOrientationEvent(){
    if(orientation == 0)document.getElementById("change").value="竖";
    else document.getElementById("change").value="横";
}
var innerWidthTmp = window.innerWidth;
//横竖屏事件监听方法
function screenOrientationListener(){
    try{
        var iw = window.innerWidth;    
        //屏幕方向改变处理
        if(iw != innerWidthTmp){
            if(iw>window.innerHeight)orientation = 90;
            else orientation = 0;
            //调用转屏事件
            screenOrientationEvent();
            innerWidthTmp = iw;
        }
    } catch(e){alert(e);};
    //间隔固定事件检查是否转屏，默认500毫秒
    setTimeout("screenOrientationListener()",500);
}
//启动横竖屏事件监听
screenOrientationListener();
</script>
</head>
<body onload="screenOrientationEvent()">
<input id="change" type="text" value=""/>
</body>
</html>