How do you limit CoffeeScript (or JavaScript) execution to a particular controller and action in Rails 3.1?

The new Rails 3.1 asset pipeline is really nice, but since all CoffeeScript (or JavaScript) files get melded down into a single file that is included in every page, it raises this question:

How do I limit the execution of my script to a particular controller or action? Is there a way within my CoffeeScript to know which controller and action was used during the request so that I can put conditional statements in my script?

Or am I approaching this the wrong way altogether?

Answers:

Answer

Trevor Burnham answers this question nicely here: How do I associate a CoffeeScript file with a view?

He says:

There are two common approaches:

  1. Make behavior conditional on the presence of a particular element. For instance, code to run a signup sheet should be prefaced with something like

    if $('#signup').length > 0

  2. Make behavior conditional on a class on the body element. You can set the body class using ERB. This is often desirable for stylesheets as well. The code would be something like

    if $('body').hasClass 'user'

And if you're interested in CoffeeScript, Trevor is working on a book that looks to be very good: http://pragprog.com/titles/tbcoffee/coffeescript

Answer

One way to restrict coffeescript to a particular view is to make a custom sprockets file for the javascript in question, similar in format to application.js. Say you call it extras.js.

//= require my_code.js.coffee

Then use javascript_include_tag "extras" to include that code in the views you want, either by making a custom layout for those views, or by using content_for()

BTW, your question stated that the rails pipeline forces you to put all your js assets in one file. That's not true. That's efficient often to avoid multiple round trips, but you can have multiple sprocket files.

Answer

Why not to put the javascript for the particular controller as a view on this controller (as they correspond there if are so specific)?

If they are general enaugh you can mark your view with classes, ids or data (html5) and make your javascript look for that (so you can reuse your code).

Answer

what i normally do is to have a yield :js under the javascripts in my layout and when I need a specific script it, I load it directly from my view with:

content_for :js do
    javascript_include_tag "myscript"
end
Answer

If you are using the gon gem for your vars in coffee script you can use this pattern:

Put a flag for every action in the controller:

  def index
    @gps_coords = GpsCoord.all

    # Flag for the CoffeeScript to decide which part to run
    gon.index = true;
  end

  def show
    @gps_coord = GpsCoord.find(params[:id])

    gon.lat = @gps_coord.latitude
    gon.lon = @gps_coord.longitude

    gon.show = true;
  end

In the correlating coffee script use those flags to distiguish between the both actions:

  # index action?
  if gon.index? 
    first_coord = gon.gps_coords[0]
    map.setView([first_coord.latitude, first_coord.longitude], 15);

  # show action?
  if gon.show?
    map.setView([gon.lat, gon.lon], 15);

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