The more ajaxified application, the more fun it is to use. But it is also more painful do develop. What is written below is my approach to pairing Rails and Ajax. It’s a mix of tips I found over the net on blogs and forums. I use jQuery for JavaScript, but I don’t use jRails or any JS/Ajax helper methods provided by Rails. Note that all Javascript/HTML code presented here can be used even if you dont use Rails or Ruby as your web development platform. Let’s begin.

Rails is RESTful

Thanks to Rails' RESTfulness the only thing to take care of server side is setting proper response in controllers' actons.

class PostsController < ActionController::Base
  def index
    @posts = Post.find :all
    respond_to do |format|
      format.html
      format.xml { render :xml => @posts.to_xml }
    end
  end
end

Rails decides which format block to call basing on routes defined in routes.rb file (map.connect ‘:controller/:action/:id.:format’) and accept headers sent with request by the client.

In most cases we want Ajax requests to trigger format.xml blocks in our controllers' actions, so we need to set proper accept headers. Let’s do it just once with application-wide setting.

// All ajax requests will trigger the format.xml block
// of +respond_to do |format|+ declarations
$.ajaxSetup({
  'beforeSend': function(xhr) {xhr.setRequestHeader("Accept", "text/xml")}
});

Browsers’ quirks

There is something worth noting here, a problem I had once with IE and Safari. The code above may work differently in various browsers. Browser set text/html accept header by default. Here IE and Safari will append text/xml to it so you’ll get something like ‚text/html; text/xml’, while Firefox will replace text/html with text/xml and you’ll get ‚text/xml’ only. This is very important because Rails will take the first format it detects in accept header and trigger respective block in controller’s action, which will be html for IE and Safari. Here’s a fix for this that shifts application/xml (if it is present) to the beggining of accept headers array.

class ApplicationController < ActionController::Base
  before_filter :correct_safari_and_ie_accept_headers

  def correct_safari_and_ie_accept_headers
    request.accepts.sort!{ |x, y| y.to_s == 'application/xml' ? 1 : -1 } if request.xhr?
  end
end

Ajaxify your links

Here’s a quick way to ajaxify your existing links. Add this JavaScript to your application.js file.

jQuery(document).ready(function() {
  // All A tags with class 'get', 'post', 'put' or 'delete' will perform an ajax call
  jQuery('a.get').livequery('click', function() {
    var link = jQuery(this);
    $.get(link.attr('href'), function(data) {
      if (link.attr('ajaxtarget'))
        jQuery(link.attr('ajaxtarget')).html(data);
    });
    return false;
  }).attr("rel", "nofollow");

  jQuery('a.post').livequery('click', function() {
    var link = jQuery(this);
    $.post(jQuery(this).attr('href'), "_method=post", function(data) {
      if (link.attr('ajaxtarget'))
        jQuery(link.attr('ajaxtarget')).html(data);
    });
    return false;
  }).attr("rel", "nofollow");

  jQuery('a.put').livequery('click', function() {
    var link = jQuery(this);
    $.post(jQuery(this).attr('href'), "_method=put", function(data) {
      if (link.attr('ajaxtarget'))
        jQuery(link.attr('ajaxtarget')).html(data);
    });
    return false;
  }).attr("rel", "nofollow");

  jQuery('a.delete').livequery('click', function() {
    var link = jQuery(this);
    $.post(jQuery(this).attr('href'), "_method=delete", function(data) {
      if (link.attr('ajaxtarget'))
        jQuery(link.attr('ajaxtarget')).html(data);
    });
    return false;
  }).attr("rel", "nofollow");

  jQuery('a.get, a.post, a.put, a.delete').removeAttr('onclick');
});

Just add a CSS class .get, .post, .delete, or .put to a link to make turn it into an ajax-link. I recommend you use LiveQuery plugin which will automatically bind click events to new links that appear on the page (loaded with Ajax call for-example). You can optionally set ajaxtarget attibute of the link. It expects a selector of a container in which you want to place the response.

link_to 'my cool article', article_path(@article), :class => 'get', :ajaxtarget => '#article_container'

Ajaxify your forms

For this you’d need jQuery Form Plugin.

    jQuery('form.ajax').livequery('submit', function() {
      jQuery(this).ajaxSubmit();
      return false;
    });

Now all your forms that have “ajax” class will be submitted via Ajax.

CSRF and authenticity token

Rails has built-in protection from cross-site request forgery attacks. It relies on an authenticity token which Rails look for when dealing with POST, PUT or DELETE requests, so this token needs to be sent by the browser together with the request. The token is automatically added as a hidden field to any form you create with form_for method, it is also attached to links that have :method param set to :post, :put or :delete. In fact the token is added dynamically by Javascript code placed in link’s onclick attribute. However in one of code snippets above we stripped that onclick attribute from links to prevent the page reload after we click the link. Now we need to attack that token ourselves. First we will alter our application layout:

<% if protect_against_forgery? %><% end %>

Now we need to ensure that the token is sent together with ajax requests.

jQuery(document).ready(function() {
  // All non-GET requests will add the authenticity token
  // if not already present in the data packet
  jQuery("body").bind("ajaxSend", function(elm, xhr, s) {
    if (s.type == "GET") return;
    if (s.data && s.data.match(new RegExp("\\b" + window._auth_token_name + "="))) return;
    if (s.data) {
      s.data = s.data + "&";
    } else {
      s.data = "";
      // if there was no data, $ didn't set the content-type
      xhr.setRequestHeader("Content-Type", s.contentType);
    }
    s.data = s.data + encodeURIComponent(window._auth_token_name)
                    + "=" + encodeURIComponent(window._auth_token);
  });
});

We’re done, we have our ajax requests protected from CSRF attacks.

Modifing page after Ajax calls

Standard way to do page modification after Ajax call is to use Javascript code that inserts content returned by the call somewhere on the page. The other method is to put the modifying code in views that are returned by the server and just execute it in the browser. For this I’d recommend another jQuery plugin - Taconite. As the author says: “The jQuery Taconite Plugin allows you to easily make multiple DOM updates using the results of a single AJAX call. It processes an XML command document that contain instructions for updating the DOM”. Thanks to this you can for example easily use flash messages in your Ajax views.

Let this be a part of your usual layout:

Now let this be your taconite layout you’d use when returning views for Ajax requests:

<% if flash[:notice] %>

    <%= flash[:notice] %>

<% end %>
<%= yield %>

This will display flash notice messages with fade-in effect after Ajax requests. Similarly you can update other elements of the page.

What’s in your toolbox?

I would love to hear from you on how you deal with Ajax in your web applications. What libraries/plugins do you use?