RoR Class vs Instance variables, and relaying a value to partial - ruby-on-rails

Question

I have a controller "mainpage", with a correspondingly named view. The controller creates a #myLocalSuites variable, and the view includes the following line:
<li class="active"><%= link_to "Perforce", :action => 'renderp4', :remote => true, :localSuites => #myLocalSuites %></a></li>
Routing is defined such that clicking this link_to calls renderp4.js.erb to render a partial within the mainpage view:
$('#MainPage').replaceWith('<%= escape_javascript render "perforce_sync/perforceSync" %>')
where _perforceSync partial includes:
<%= select_tag "perforceSuites", options_for_select(*MYOPTIONSVARIABLE*), {:class => 'form-control', :size => "20", :multiple => true} %>
Where *MYOPTIONSVARIABLE* needs to be myLocalSuites as cascaded down from the mainpage view/controller.
Having tried everything I can think of, and failed - can someone please show how to modify the above snippets to use the required variable in the PerforceSync partial? Everything I've tried seems to produce something along the lines of:
ActionView::Template::Error (undefined method `map' for nil:NilClass):
An example of what I've tried. I don't think I'm a million miles off, but...
<li class="active"><%= link_to "Perforce", :action => 'renderp4', :remote => true, :localSuites => #myLocalSuites %></a></li>
$('#MainPage').replaceWith('<%= escape_javascript render "perforce_sync/perforceSync", :suitesLocally => params[:localSuites]%>')
<%= select_tag "perforceSuites", options_for_select(params[:suitesLocally]), {:class => 'form-control', :size => "20", :multiple => true} %>
Thanks! :)

Answer 1

In response to your comment, there are two things you can do here. One way is to simply render some dynamic JS on page load, and then use javascript to show that data at a later point.
If this data however is to depend on user actions after the page has loaded, you must make another request to the server using AJAX.
The first way might look like this:
<script>
var my_data = "<%= #some_data %>";
//#some_data could be set by the controller action for example
$('button').click(function() {
$('div.content_container').text(my_data);
});
</script>
The second way would look like this:
<script>
$('button').click(function() {
$.ajax({
url: '/some_resource/id.json',
data: {param1: 'some_user_data'}
}).done(function(data) {
$('div.content_container').text(data);
});
});
</script>
The data option for the ajax call allows you to pass parameters back to the server, so you can send some data provided by the client. Documentation for jquery ajax is here if you want to see other options.
The .done callback gets fired when the client receives a response from the server, and the function parameter is the data returned.