获取当前设备的屏幕宽度

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<!DOCTYPE html>
<html>
<head>
	<meta charset="utf-8">
	<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1,maximum-scale=1,user-scalable=no">
	<title>获取当前设备的屏幕宽度</title>
	<script>
		var deviceWidth = parseInt(window.screen.width);  //获取当前设备的屏幕宽度
		var deviceScale = deviceWidth / 640;  //得到当前设备屏幕与640之间的比例，之后我们就可以将网页宽度固定为640px
		var ua = navigator.userAgent;
		//获取当前设备类型（安卓或苹果）
		if (/Android (\d+\.\d+)/.test(ua)) {
			var version = parseFloat(RegExp.$1);
			if (version > 2.3) {
				document.write('<meta name="viewport" content="width=640,initial-scale=' + deviceScale + ', minimum-scale = ' + deviceScale + ', maximum-scale = ' + deviceScale + ', target-densitydpi=device-dpi">');
			} else {
				document.write('<meta name="viewport" content="width=640,initial-scale=0.75,maximum-scale=0.75,minimum-scale=0.75,target-densitydpi=device-dpi" />');
			}
		} else {
			document.write('<meta name="viewport" content="width=640, user-scalable=no">');
		}
	</script>
</head>
<body>

</body>
</html>