js获取本地即将上传文件的大小 [兼容IE、FF、chrome]

js获取本地即将上传文件的大小：

<input type="file" onchange="fileChange(this);" />
<script type="text/javascript">
var isIE = /msie/i.test(navigator.userAgent) && !window.opera;
function fileChange(target) {
	var fileSize = 0;
	if (isIE && !target.files) {
		var filePath = target.value;
		var fileSystem = new ActiveXObject("Scripting.FileSystemObject");
		var file = fileSystem.GetFile (filePath);
		fileSize = file.Size;
	} else {
		fileSize = target.files[0].size;
	}
	var size = fileSize / 1024;
	alert('文件大小: '+size+'KB');
}     
</script> 

[演示]