From the link you provided:
Both the JavascriptHelper and the AjaxHelper are deprecated, and the
JsHelper + HtmlHelper should be used in their place. See The Migration
Guide
On Js helper page:
Since the beginning CakePHP's support for Javascript has been with
Prototype/Scriptaculous. While we still think these are an excellent
Javascript library, the community has been asking for support for
other libraries. Rather than drop Prototype in favour of another
Javascript library. We created an Adapter based helper, and included 3
of the most requested libraries. Prototype/Scriptaculous,
Mootools/Mootools-more, and jQuery/jQuery UI. And while the API is not
as expansive as the previous AjaxHelper we feel that the adapter based
solution allows for a more extensible solution giving developers the
power and flexibility they need to address their specific application
needs.
echo $this->Html->script('jquery'); // Include jQuery library
And also take a look at the jQuery AJAX pagination example.