How Do I Validate The File Type Of A File Upload?

- 1 answer

I am using <input type="file" id="fileUpload" runat="server"> 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).

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).



Seems like you are going to have limited options since you want the check to occur before the upload. I think the best you are going to get is to use javascript to validate the extension of the file. You could build a hash of valid extensions and then look to see if the extension of the file being uploaded existed in the hash.


<input type="file" name="FILENAME"  size="20" onchange="check_extension(this.value,"upload");"/>
<input type="submit" id="upload" name="upload" value="Attach" disabled="disabled" />


var hash = {
  'xls'  : 1,
  'xlsx' : 1,

function check_extension(filename,submitId) {
      var re = /\..+$/;
      var ext = filename.match(re);
      var submitEl = document.getElementById(submitId);
      if (hash[ext]) {
        submitEl.disabled = false;
        return true;
      } else {
        alert("Invalid filename, please select another file");
        submitEl.disabled = true;

        return false;