jQuery AJAX and multipart form handling

I recently had need to submit a web form with file fields via AJAX. The application uses jQuery and was already submitting forms just fine without file fields using the .serialize() method to pass data to a jQuery.ajax() call. That didn’t seem to handle the file fields, though. Searching the internet, I found a solution using the browser built in FormData object.

The jQuery.ajax() method will accept a FormData object for the data parameter. To make this work requires setting the processData and contentType parameters to false. The enctype parameter should be set to multipart/form-data, just like the form would have. Putting this all together, the solution looks something like:

var $form = jQuery('form');
$form.on('submit', function(event){
  var request = {
    method: $form.attr('method') || 'POST',
    url: $form.attr('action') || window.location.href
    request.enctype = $form.attr('enctype');
  if(window.FormData && $form.attr('enctype') === 'multipart/form-data'){
    request.contentType = false;
    request.data = new FormData($form[0]);
    request.processData = false;
    request.data = $form.serialize();
  jQuery.ajax(request, function(response){

It falls back to the .serialize() method if it doesn’t need FormData or the browser doesn’t support it. This worked well enough for our needs.