2. Rails and XMLHttpRequests
• Rails provides multiple ways to handle the actual
response building from re-rendering the html to
simply rendering json/xml/whatever-serialized.
• It also provides a handy way to specify some link
or a form that has an ajax action.
• Adding :remote => true to i.e. a link_to-helper
will transform the link to fire an XMLHttpRequest
instead of following the link.
• This allows pure Rails applications to be built in a
way that degrades gracefully if the client doesn’t
have JavaScript enabled.
http://extremia.fi/ • http://extremia.net/
3. Handling the request
• Rails provides a lot of control over how to
handle MLHttpRequests:
– It’s possible render a partial view and return that
using some logic already defined on the client to
update the DOM, render JSON and parse it into
the DOM on the client,
– or return JavaScript containing all the logic
required to update the currently visible page on
the client.
http://extremia.fi/ • http://extremia.net/
4. Handling the request
• To check whether the request is an XHR one Rails
provides a helper called request.xhr?
– It checks the request for ‘X-Request-With’ =
‘XMLHttpRequest’ header. So if your application
handles ajax for example by re-rendering a partial
view you could use request.xhr? to check whether the
whole page should be rendered or not.
• A bit cleaner way is to use respond_to with
format. By default XHR-requests made using the
Rails helpers with :remote => true can be handled
using format.js.
http://extremia.fi/ • http://extremia.net/
5. Handling the response
• Apart from returning JavaScript that updates
the DOM straight from server the response
can be handled using events .
• Requests that happen using the Rails
unobtrusive JavaScript (ie. :remote => true)
fire events
(ajax:beforeSend, ajax:complete, ajax:success
, ajax:error) allows you to use for
example, jQuery to bind to them, updating the
DOM based on the request status.
http://extremia.fi/ • http://extremia.net/
6. Handling the response
• Rails also allows you to return JavaScript that’s
executed on response, allowing you to write
code for updating the DOM to be returned
with the changed data.
• Handling XHR this way probably won’t scale
too far as the response is always created on
the server side and requires more data to be
sent over the wire in comparison to serialized
json/xml and client side rendering.
http://extremia.fi/ • http://extremia.net/
