Ruby on Rails | Collection_Select [Value] -> Param

Question

Got a (hopefully) easy one:

Ruby partial view with a collection_select, need the value of that selection (var name = 'submod') passed as a param up to controller. Literally just stuck on how to get from collection_select/onchange() to named param.

html.erb code:

<% @modName = locals[:moduleName] %>
<% @id = locals[:id] %>

<%= form_with url: admin_command_path() do |f| %>
    <%= collection_select(@refcode, :Code, Command.where(FLD: @modName), :Code, :Definition, options ={prompt: true}, html_options = {:onchange => "updateSubMod(this.value)"}) %>
    <br /><br />
    <button class="btn_new">
        <%= link_to "Execute", new_admin_command_path(mod: @modName, submod: @refcode, id: @id) %>
    </button>
<% end %>

The onchange function works as expected, so feel free to make use of that to solve for param:

<script>
    function updateSubMod(Code) {
        var submod = Code
        console.log(submod, '********************')
    }
</script>