<script type="text/javascript">
var phoneWidth = parseInt(window.screen.width);
var phoneScale = phoneWidth/640;

var ua = navigator.userAgent;
if (/Android (\d+\.\d+)/.test(ua)){

var version = parseFloat(RegExp.$1);
// andriod 2.3
if(version>2.3){
    document.write('<meta name="viewport" content="width=640, minimum-scale = '+phoneScale+', maximum-scale = '+phoneScale+', target-densitydpi=device-dpi">');
    // andriod 2.3以上
}else{
    document.write('<meta name="viewport" content="width=640, target-densitydpi=device-dpi">');
}
// 其他系统

} else {

document.write('<meta name="viewport" content="width=640, user-scalable=no, target-densitydpi=device-dpi">');

}
</script>

如上代码，使页面限制成640px宽度，但是在有的设备上是失效的，有的是高度好像没跟着缩小~
求解