How to check an Ajax request in cakephp?
var $components = array('RequestHandler');
$this->RequestHandler->isAjax()
You can find more information about the RequestHandler component here
Without the use of components you can use something like this:
$this->params['isAjax'];
This will return a bool.
If you simply want to check the function of the php side, try:
$this->log('some debug',LOG_DEBUG);
then check app/tmp/logs/debug.log.