url helper in model.js.erb.cofee (Sprockets::Context)

hello,
I am writing a js/coffee file that gets erb handling and I need to use
a url helper inside this file
if write
..
      url: '<%= url_for(:action => :index) %>'

I get an error:
NoMethodError Exception: undefined method `url_for' for #<#<Class:
0xbdbb068>:0xeed1eb8>

self.class

#<Class:0xbdbb068> < Sprockets::Context

How do I make url_for accessible in Sprockets::Context?

thank you.

http://stackoverflow.com/questions/7517140/why-are-the-actionviewhelpersurlhelper-not-available-in-the-assets-pipeline

Best regards

Peter De Berdt