Page not updating when using jquery/ajax

I'm making a web app that lets people add courses to a shopping cart. I have a Cart model that has_many LineItems.

In the cart, I have an ajaxified button that lets people remove individual line items. This works fine. Here's the code for that:

_line_item.html.erb:

<div class="delete_line_item"><%= button_to 'Delete', line_item, 
{:method => :delete, :remote => true} %></div>

The line_items controller:

  def destroy
    @user = current_user
    @line_item.destroy
    @cart = @user.cart

    respond_to do |format|
      format.html { redirect_to(root_path) }
      format.js
      format.xml  { head :ok }
    end
  end

Then, the destroy.js.erb file, located within my views/line_items folder:

$("#cart").html("<%= escape_javascript(render(@cart)) %>");

I want to do something similar for emptying out the cart. To do this, I'm using the update action in the carts controller. Here are the corresponding code chunks for this:

<div class="empty_cart"><%= button_to 'Empty cart', cart, {:method => :put, :remote => true, 
:confirm => 'Are you sure?'} %></div>

#carts controller
  def update
    if @cart.line_items
      @cart.line_items.each do |item|
        item.destroy
      end 
    end 

    respond_to do |format|
      if @cart.update_attributes(params[:cart])
        format.html { redirect_to(root_path, :notice 开发者_运维知识库=> 'Cart emptied.') }
        debugger
        format.js
        format.xml  { head :ok }

Finally, here's the update.js.erb file I've placed within my views/carts folder:

$("#cart").html("<%= escape_javascript(render(@cart)) %>");

The problem is that when I try to empty the cart, the request goes through (in that when I refresh the page, the cart is empty), but the change doesn't appear immediately upon clicking. This makes me think that my browser is simply not rendering the .js.erb file. Do I need to place the update.js.erb file in a different folder or rename it? Or something else going on?

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Instead of using the update action, why don't you just use the destroy action for the cart instead of using the update? That's what I did, and it worked.