Rails 3.1/Sprockets: Injecting controller variables (or helpers) into javascript assets

Question

I have an action with

def new 
  @test_var = 'i want this to show'
end

All I want to do is inject that into the javascript called for that page. For example:

#app/assets/javascript/my_model.js.coffee.erb
$ ->
  console.log('<%= @test_var %>')

I'm guessing this doesn't work because that the coffeescript/erb is compiled before the controller is accessed...so, if I wanted to inject controller variables into a JavaScript file (client side - NOT accessed via ajax) in 3.1, how should I go about doing it?

Answer 1

I believe the problem is that you're thinking about the asset pipeline all wrong... asset being the operative word.

It's not a view pipeline. Other things which are assets? images & css files, things which can be preprocessed and then served as-is. The erb/preprocessing of your assets doesn't occur on each pageload/request, rather it occurs on startup/filechange so in production said assets can be optimised, cached and served statically.

You could probably figure out a way to achieve it using Live Compilation (see section 4.2 of http://guides.rubyonrails.org/asset_pipeline.html) but as the docs say:

This mode uses more memory and is lower performance than the default. It is not recommended.

The bad answer would be 'inject the javascript into your view', but decoupling your javascript from your rails controllers/views is a good idea.

A better answer would be to have an asset folder containing all of your controller javascripts, and use some "what page am I on?" javascript to determine whether to run the code or not.

Here's some answers that explain various approaches to this:

Rails 3.1 asset pipeline: how to load controller-specific scripts?

Using Rails 3.1, where do you put your "page specific" javascript code?