Check file type when form submit ?

Instead of using onsubmit, use jQuery's submit handler, and validate using some javascript like the following:

js:

function getExtension(filename) {
  var parts = filename.split('.');
  return parts[parts.length - 1];
}
function isImage(filename) {
  var ext = getExtension(filename);
  switch (ext.toLowerCase()) {
    case 'jpg':
    case 'gif':
    case 'bmp':
    case 'png':
      //etc
      return true;
  }
  return false;
}
function isVideo(filename) {
  var ext = getExtension(filename);
  switch (ext.toLowerCase()) {
    case 'm4v':
    case 'avi':
    case 'mpg':
    case 'mp4':
      // etc
      return true;
  }
  return false;
}
$(function() {
  $('form').submit(function() {
    function failValidation(msg) {
      alert(msg); // just an alert for now but you can spice this up later
      return false;
    }
    var file = $('#file');
    var imageChosen = $('#type-1').is(':checked');
    if (imageChosen && !isImage(file.val())) {
      return failValidation('Please select a valid image');
    } else if (!imageChosen && !isVideo(file.val())) {
      return failValidation('Please select a valid video file.');
    }
    // success at this point
    // indicate success with alert for now
    alert('Valid file! Here is where you would return true to allow the form to submit normally.');
    return false; // prevent form submitting anyway - remove this in your environment
  });
});

html:

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

<form action="/gallery/create" method="post" enctype="multipart/form-data">

  <label>Type:*</label>

  <label for="type-1">

     <input type="radio" checked="checked" value="1" id="type-1" name="type">Image

    </label>

  <label for="type-2">

   <input type="radio" value="2" id="type-2" name="type">Video

    </label> <br />

  <label class="itemdetailfloatL required" for="file">File:*</label>

  <input type="hidden" id="MAX_FILE_SIZE" value="8388608" name="MAX_FILE_SIZE">

  <input type="file" tabindex="5" class="text-size text" id="file" name="file">

  <br/>

  <input type="submit" value="Create" id="submit" name="submit">

</form>

#viastudy