Route helpers in asset pipeline

using Rails 3.1.0.rc4, I'm trying to access a route helper in a javascript file (event.js.erb in this case) and it seems like they are not loaded at that moment. When requesting the merged /assets/application.js file, I get:

throw Error("NameError: undefined local variable or method `events_path' for #<#<Class:0x00000001580010>:0x00000003191510>\n  (in /<...>/app/assets/javascripts/event.js.erb)")

Any idea how to access the route helper in there?

UPDATE: Now there is a gem that does this for you: js-routes

The problem is that Sprockets is evaluating the ERB outside of the context of your Rails app, and most of the stuff you're expecting isn't there.

You can add things to your Sprockets context like so:

Rails.application.assets.context_class.class_eval do
  include Rails.application.routes.url_helpers
end

That's all well and good, but getting the helpers that require an id to work is a little trickier. I'm going to use a technique called a URI Template:

var event_path = "<%= CGI.unescape event_path('{event_id}') %>";

which returns /events/{event_id} which you could render into a url using an object like { event_id: 1 }. See SugarJS's String#assign method as example implementation of this. You could also roll your own like I did.

You could move the file to views where it has access to the proper context, then pull it down to the client from a JS source tag. Referring to MyRailsApp::Application.routes.url_helpers may not be the best if you are writing an engine.