如何使用JavaScript验证文件的大小？

Question

当单击页面上的上传按钮时...要检查在文件上传控件中选择的文件大小，并在文件大小超出限制时停止上传按钮的回发...使用jquery / javascript的方法是什么？

Answer 1

Although it's hardly a foolproof way, some browser check if you have a hidden input element specifying the maximum filesize like so:

<input type="hidden" name="MAX_FILE_SIZE" value="1048576" />

[edit]It seems that this type of checking was never actually implemented by one of the main browsers. It was merely hoped that they did.

In that case you can only limit the file upload size (clientside) with flash, silverlight, java or some other clientside plugin.

Answer 2

You can't, you must use server-side PHP or ASP[.NET] to do so. If it is possible, crackers will be stealing files.

Answer 3

There is no way to implement this in a pure Javascript solution, since for security reasons, Javascript doesn't have access to your local filesystem. The only fool-proof way to do what you want is on the server. Depending on the technology you use, you may be able to intercept the request while it's still being sent and kill it based on the Content-length header.