Javascript gem "format.js"

I want to upload file with javascript AJAX but I have an error InvalidAuthenticutyToken when I correct my code like I see on many website another error appear : Unknown format in :

if @personal.save
    format.js
end

In my IDE the .js do an error : cannot find js

I think I miss a gem. My installed gems in order to use javascript are :

gem 'coffee-rails',          '~> 4.1.0'
gem 'coffee-script-source',  '1.8.0'
gem 'jquery-rails'
gem 'turbolinks'
gem 'jbuilder',              '~> 2.0'

And my form is

<%= bootstrap_form_for @personal, :html => {:multipart => true}, :remote => true do |f| %>
<div class="modal-body">
  <%= f.text_field :trigramme, label: "Trigramme" %>
  <%= f.text_field :nom, label: "Nom" %>
  <%= f.text_field :prenom, label: "Prenom" %>
  <%= f.text_field :poste, label: "Poste" %>
  <%= f.text_field :arrivee, label: "Arrivee a OCTO" %>
  <%= f.text_area :bio, label: "Bio", :rows => "5" %>
  <%= f.file_field :img, label: "Photo" %>

</div>
<div class="modal-footer">
  <%= f.submit class: "btn btn-primary" %>
  <%= link_to "Cancel", "#", class: "btn", data: {dismiss: "modal"} %>
</div>

It's weird because when I have the error of Invalid AuthenticutyToken my image is correctly uploaded in database but I have the error. I have some js.erb file that print a popup with the form. I have tried remotipart but nothin happen I have again the error.

Do I miss a gem in order to use javascript due to second error unknownFormat? What is my problem ? Do you have a clue?

via Chebli Mohamed