AJAX a form submission with Rails 3.2 - ruby-on-rails-3

Question

This is my form, and it works fine, but now I want to AJAX it.
<%= form_tag variant_path(variant.id), :method => :put, :class => 'update_inv_form' do %>
<%= text_field_tag :inventory_quantity, variant.inventory_quantity %>
<%= submit_tag 'Update' %>
<% end %>
When I add the :remote => true attribute the form successfully submits via AJAX (I can see it happening on the server and I can see the changes when I refresh the page). I want to update the view properly to show the changes without refreshing the page. This is my update action: (Note that I am not working with ActiveRecord Models here.)
def update
variant = ShopifyAPI::Variant.find(params[:id])
variant.inventory_quantity = params[:inventory_quantity]
variant.save
redirect_to root_path
end
UPDATE
Thank you to the answer that helped me figure this out turns out the solution is exactly as he said, however I ran into a small problem. The view I wanted to update lives in app/views/home/index.html.erb and I was dealing with this: Variants#update. (Variants controller, update action)
I was putting my update.js.html in the same directory that my view was: app/views/home and my server was throwing a 500 error: Missing Template. Turns out, I had to create an app/views/variants/ directory and put the update.js.html file in there. Problem solved.

Answer 1

You'll need to change your action to respond to the JS format:
def update
#variant = ShopifyAPI::Variant.find(params[:id])
#variant.inventory_quantity = params[:inventory_quantity]
#variant.save
respond_to do |format|
format.html { redirect_to root_path }
format.js
end
end
You can then create an update.js.erb file with JavaScript that will update the page. Let's say you have a _variant.html.erb partial, you could append the variant to a div like this (assuming you are using jQuery):
$('.variant-list').append('<%= escape_javascript(render(:partial => "variant", :object => #variant)) %>');
update
Here's an example of how you would use the update.js.erb' file (Note: I have not tried this code). Let's say you have the following code in yourindex.html.erb`:
<ul class="variants">
<li id="101">Variant 1</li>
<li id="102">Variant 2</li>
<li id="103">Variant 3</li>
</ul>
Your updated.js.erb could look something like this:
$('.variants #<%= #variant.id %>').text('<%= #variant.title %>');
What this does is find the variant you just updated in the list, and change the variant title to the new one.