ujs problem

gistfile1.rb

def create
    @cart = current_cart
    product = Product.find(params[:product_id])
    @line_item = @cart.add_product(product.id)

    respond_to do |format|
      if @line_item.save
        format.html { redirect_to(store_url)}
        format.js { @current_item = @line_item }
        format.xml  { render :xml => @line_item, :status => :created, :location => @line_item }
      else
        format.html { render :action => "new" }
        format.xml  { render :xml => @line_item.errors, :status => :unprocessable_entity }
      end
    end
  end

the ujs template has only this line:

alert("hey there, the cart id is <%= escape_javascript(@current_item.quantity) %>");