title: How do I Validate the File Type of a File Upload?
body: <p>I am using <code>&lt;input type="file" id="fileUpload" runat="server"&gt;</code> to upload a file in an ASP.NET application. I would like to limit the file type of the upload (example: limit to .xls or .xlsx file extensions). </p>
  
  <p>Both JavaScript or server-side validation are OK (as long as the server side validation would take place before the files are being uploaded - there could be some very large files uploaded, so any validation needs to take place before the actual files are uploaded).</p>