Using jquery in ajax request to get javascript response UJS

In Rails, you can respond to different MIME types, including application/javascript. You often use this MIME type for ajax requests to send javascript back to the browser to be evaluated. The respond_to symbol is :js.

I see examples like this:

<%= form_tag('/articles', remote: true) do %>
  ...
<% end %>

<%= link_to "Delete article", @article, remote: true, method: :delete %>

The rails.js file finds the remote links, forms, and inputs, and overrides their click events to submit to the server via AJAX.

Server has something like this:

  respond_to do |format|
    format.js 
  end

In my situation, I need to do the request in jQuery, so I cannot use the remote: true feature.

<%= form_for @tag do |f| %>
  <%= f.fields_for :taggings, f.object.taggings.build do |taggings_builder| %>
    <%= taggings_builder.hidden_field :tagging_flag, value: @contact.flag %>
  <% end %>
  <%= f.text_field :name, class: 'form-control', placeholder: 'Add a tag and press enter' %>
<% end %>

My problem is when I specify contentType as 'application/javascript' in jquery ajax method, no form data is sent to server. I even inspected it in Network tab on chrome. When I remove the contentType property, the form data is submitted to server but the the content type is not 'application/javascript'. It is 'application/x-www-form-urlencoded; charset=UTF-8'.

My jquery looks like this:

$view.on('keypress','form#add-tag input#tag_name', function(e){
   var $form = $(this).closest('form');
   var key = e.which;

   if(key == 13){

      $.ajax({
         type: "POST",
         data: $form.serialize(),
         contentType: 'application/javascript',
         url: $form.attr('action'),
         beforeSend: function() {
           $('.loading').show();
         },
         complete: function(){
           $('.loading').hide();
         },
         success: function(resp){
         }
      });


     return false;
   }
})

How can I send the form data to server with the content type of 'application/javascript'?