23 October 2014

CoffeeRoutes - Rails named routes in Coffeescript

Fairly frequently I find myself in the posiiton that I need to make an AJAX call to my rails app to send or fetch some piece of data or another. To do this I need to know which URL to hit, and which HTTP verb to use to make the request.

If I’m submitting a form via AJAX, that’s no problem at all. Both the url and the method are right there in the form declaration, we can just do.

form = $('form.my_form')
  url: form.attr('action')
  type: form.attr('method')

What about when we’re not submitting a form though? What if we want to pull some data from a URL, or submit some data without having a form? There’s a few hacks that I’ve used in the past, none of them are much good.

The Workarounds

Hack #1: Hard code the URL. This works brilliantly until you change the route, then you have to hunt through your coffeescript to find all of the places you’ve hardcoded the URL. This can be particularly annoying if you’ve had to concatenate in some parameters to your URL.

Hack #2: Put a submission URL in a data attribute. In the cases where the URL updates a particular resource, for example getting more information about an item from a list, you can place the URL in a data attribute on that list item.

  - for item in items
    %li.list__item{:data => {:show_url => item_path(item)}= item.name
$('li.list__item').on 'click', ->
  itemUrl = $(this).data('showUrl')
    url: itemUrl...

Hack #3: Global containing URLs. An object placed inline with on your page that contains URLs that you might need on that page request.

  window.ajaxUrls = {
    "create" : #{items_path}, 
    "poll": #{poll_items_path}

The Solution

The solution actually builds on Hack #3, but formalises it in a way that doesn’t require hacky inline JS and presents a nice friendly wrapper and some helper methods.

Rails has already has a nice way to print out your application’s routing table, it uses it whenever you type rake routes or encounter a routing error. With this in mind I set about finding out how rake routes worked. Working backwards from the rake task I found ActionDispatch::Routing::RoutesInspector along with it’s friends ActionDispatch::Routing::HtmlTableFormatter and ActionDispatch::Routing::ConsoleFormatter. Ignoring the warning at the top of the RoutesInspector “# People should not use this class.” I set about building a formatter class that would output a nice JSON string of routes.

JSON string produced, now we need to inject thst into our page and build a few helper methods around the data. coffee_routes.coffee.erb creates a global CofeeRoutes object and gives it a parameter of routes which contains our JSON object.

Next the path function was added to CoffeeRoutes to find the named route from the #routes and substitute in any parameter varaibles that could be passed in as an object along with the name of the route. Finally, a set of global helpers is created so that you can just type poll_item_path({"id" : 5}) for example anywhere in your coffeescript/javascript.


  1. Include coffee_routes in the Gemfile for your Rails app
  2. Add #= require coffee_routes to your application.coffee
  3. Access your named routes in Coffeescript
project_item_path({"project_id" : "project-awesome", "id" : 5})
=> "/projects/project-awesome/items/5"


Get the source on Github.