Simple Ajax Update in Rails 3

There have been several updates to the way Rails 3 interacts with Ajax.

One big change was the switch from prototype to Jquery as the standard Javascript library. Having spent a short time with Jquery, I can see how it is much more elegant and easier to understand, at least superficially. I am not a Javascript expert, but I've done a fair bit of "raw" coding accessing and manipulating the DOM, enough to appreciate the power of Jquery.

Here are the minimal code snippets to update an element in a web page with an Ajax call using the new syntax.

In the view:
<%= link_to "test", { :action => 'testajax' }, :remote => true %>
<div id='testdiv'></div>

The :remote => true indicates an Ajax link.  We are going to update the div testdiv.

In the controller, define a function to handle the call:
def testajax
  @testdata = "ajaxy data"
end

Create a new view file for the javascript response (in this case named testajax.js.erb):
$("#testdiv").html("<%= @testdata %>");

This is Jquery Javascript code, but you can use embedded ruby to pull in instance variables from the controller.  We are selecting the html content of the element with ID testdiv, then updating it with the data set in the controller "ajaxy data".