Rails - updating div w/ Ajax and :remote => true - ruby-on-rails

Question

I've followed this Railscast on submitting a form via Ajax and updating a div without reloading the page, but I'm having trouble with one portion of it.
Ryan has $("#products").html("<%= escape_javascript(render(#products)) %>"); in an index.js.erb file to update the #products div when the form is submitted. I'm struggling to understand whether an instance variable like #products is relevant for my situation, or if I can simply substitute it for a URL.
I'm trying to do the same thing as Ryan in this screencast, but instead of display search results I just want to display the updated value.
In show.html.erb I have:
<% #project.project_todos.order("created_at DESC").where(:status => false).each do |todo|%>
<%= form_for todo, :remote => true, :"data-replace" => "#dueon" do |f| %>
<%= f.text_field :due %>
<%= f.submit :class => "primary", :value => "Add" %>
<% end %>
<div id="dueon">
<%= render "duedate", :todo => todo %>
</div>
<% end %>
The partial _duedate.html.erb has one line in it: <%= todo.due %>
So in my index.js.erb I currently have this: $("#dueon").html("<%= escape_javascript(render("_duedate")) %>"); but it's clearly not working. Do I have to use a variable here in place of the _duedate? And if so, how would I set this up in the controller? I mean what does the variable have represent?
Also, for what it's worth, the partial is rendering correctly and displaying the todo.due value...it's just not updating when I submit the form.
ProjectsController:
def show
#project = Project.find(params[:id])
# Display the form to create a new todo
#project_todo = ProjectTodo.new
respond_to do |format|
format.html # show.html.erb
format.json { render :json => #project }
end
end

Answer 1

Try this
in you controller action , (say sample_action)
def sample_action
#todos = #your code
respond_to do |format|
format.js
end
end
and you have a sample_action.js.erb
$("#dueon").html("<%= raw escape_javascript(render(:partial => 'duedate')) %>")
then inside the partial, you have access to the new #todos instance variable
HTH

Answer 2

I will answer you separately as I believe your entire setup should be little change (IMO, this might not be the case)
I think you should have a todos controller with a project belongs to it,
--- models ----------------
class Project < ActiveRecord::Base
has_many :todos
end
class Todo < ActiveRecord::Base
belongs_to :project
end
---- routes ---------------
resources :projects do
resources :todos do
end
end
---- controllers ----------
class ProjectsController < ApplicationController
end
class TodosController < ApplicationController
def new
#project = Project.find(params[:project_id])
#todos = #project.todos.build
end
end
in your view (views/todos.html.erb)
<%= #project.name %>
<%= form_for([#Project, #todos]) do |f| %>
#todo form code
<% end%>
As per the relation, project has many todos, its always clear to show the project details in the todo add screen, rather than allowing users to add new todos from project screen.
and again, this is my personal view, feel free to ask any questions :)