<HTML>
<head>
<title>js获取文件大小</title>
<meta http-equiv="content-type" content="text/html;charset=utf-8" >
<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 / 1024/1024;
alert(‘文件大小: ‘+size+‘MB‘);
}
</script>
</head>
<body>
<input type="file" id="oFile" onchange="fileChange(this);" >
<input type="button" value="获取文件大小" onclick="testFileSize();">
</body>
<HTML>原文：http://my.oschina.net/u/2001537/blog/354123