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Ajax and Rails, making it work

Every time I need to add some Ajax to a Rails project I need to look up documentation and search through all my earlier files to see how I did it. Maybe this is because I’m old and was doing javascript (which I hate BTW) the old-fashioned way so getting my head around the Rails way might be more difficult, I don’t know, but it’s a pain in the arse, so I’m writing a little blog post so I can refer to it and hopefully it’ll help other people too.

How it works

To me, Ajax in Rails is needlessly convoluted, but here’s how it works:

  1. You create a link with link_to and set the remote option to true
  2. In your controller, for that link, create a format.js response
  3. Create a javascript file with the same name as the method the link responds to
  4. In that javascript file, put the js code you want Rails to execute when you click the link


This is a simple issue where I need to hide or show a column based on the value of a cookie which I’ve previously put into an instance variable:

The link

# 1
= link_to "<span class='btn btn-sm btn-primary'>eye-icon</span>".html_safe, users_flip_show_dogtag_path, title: icon_title, remote: true

The controller method

# 2
def flip_show_dogtag
   if cookies[:show_library_dogtags].to_i == 1
     set_dogtag_to = '0'
     set_dogtag_to = '1'
   cookies.permanent[:show_library_dogtags] = set_dogtag_to
   @dogtag_show_value = set_dogtag_to # we'll use this in the views
   respond_to do |format|

The javascript file

// 3
if ("<%=j @dogtag_show_value %>" == '1') {
 } else {
 // this last line simply refreshes the header with the icons which also change based on the cookie state
 $('.collection-flip-switch').html("<%=j render 'layouts/flip_collection_state' %>");


Beware of comparing integer values inside js.erb files, you might get a missing method error when the javascript helper tries to run gsub on the integer:

    NoMethodError - undefined method 'gsub' for 0:Fixnum:
       actionpack (4.0.4) lib/action_view/helpers/javascript_helper.rb:27:in 'escape_javascript'

This sucks because it means you can’t use integers for anything you need to then equate in a js.erb file but I don’t know of a workaround.

Reloading a DOM element

If you want to reload part of the page, it gets even more convoluted because you need to create a Rails template that you can call to render only that portion. Rails calls this the ‘unobtrusive’ way, but it really fragments your views and you end up with as much as 5 files to edit just to get this to work, let’s count them:

  1. the routes file, you’ll need to add a route for the link
  2. the controller file that the link method calls
  3. the view file that shows your data
  4. the js.erb (or coffescript) file that contains the actual javascript code
  5. the Rails partial file that you want to refresh

Not what I would call unobtrusive at all but there you go.

So in our earlier example, lets refresh part of the page.

Refreshing part of the page

All of the above stays the same, but we need 2 things to make the refresh happen:

  1. an element that we will refresh
  2. the Rails partial that will contain the data that we will reload

In our view file we create an element (generally a div) that we will refresh, it might look like this:

# 1
  = render 'layouts/flip_collection_state'

The Rails partial

- if cookies[:show_library_dogtags].to_i == 1
   - dogtag_icon = "<i class='icon-eye-open'></i>"
   - dogtag_icon = "<i class='icon-eye-close'></i>"
= link_to "<span class='btn btn-sm btn-primary'>#{dogtag_icon}</span>".html_safe, users_flip_show_dogtag_path, title: icon_title, remote: true

The bit in the js.erb that actually refreshes the DOM element:

$('.collection-flip-switch').html("<%=j render 'layouts/flip_collection_state' %>");

In this case the partial only contains a link and the logic to represent the right icon depending on a cookie value (I’ve stripped some other code that also gets refreshed to keep things simple).


So, not very unobtrusive at all and too many moving parts to remember every time.

Feel free to refer to this nifty guide the next time you need to use Ajax in Rails, I know I will :)

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