Use coffeescript or javascript in rails form to grab model attribute

I am working on a Rails app and need some help with coffeescript which I'm not very good at.

I have a form with a field called location_id using a collection in Rails.

<%= f.grouped_collection_select :location_id, Region.order(:area), :active_locations, :area, :id, :location_name_with_address, {include_blank: true}, class: 'select' %>

On the Location model there is a column named modifier which holds a value. Within my form I need to be able to grab the modifier value to evaluate it client-side to display/hide a div.

I'm starting to write my coffeescript and am able to get the id of the Location like this

$('#call_location_id').val()

But what I'm unsure of how to do is, how do I grab that id of the location, and evaluate the model attribute modifier? I'm not sure how to grab it on the client side.

I've googled and have read a lot of coffeescript snippets but can't seem to find the right direction to take.

I just need a bump in the right path so I can figure the rest out on my own.