Conditionally Execute JavaScript in the Asset Pipeline

application_controller.rb

class ApplicationController < ActionController::Base
  before_filter :set_gon

  # ...

  private
    def set_gon
      gon.page = "#{params[:controller]}_#{params[:action]}"
    end
  end
end

foo.js.coffee

if gon.page is 'foo_bar'
    $ -> 
        alert "Top o' the mornin' to ya'!"

if gon.page is 'foo_baz'
    $ -> 
        alert "... and Bob's your uncle!"

Gemfile

# https://github.com/gazay/gon
gem 'gon'

layout.html.haml

!!! 5
%html
  %body
    %h1 Foo
    = yield
    = include_gon
    = javascript_include_tag 'application'