CakePHP has a built-in JS Helper to help write aJax functions. The only catch is to include jquery in your head or cake will throw jQuery errors. Heres more information http://book.cakephp.org/2.0/en/core-libraries/helpers/js.html
Your Form:
<?php
echo $this->Form->create('User', array('default'=>false, 'id'=>'YourForm'));
echo $this->Form->input('username');
echo $this->Form->submit('Check Username');
echo $this->Form->end();
?>
The Ajax Function: ('update'=>'#na') is the id of the element you want to update in your view.
<?php
$data = $this->Js->get('#YourForm')->serializeForm(array('isForm' => true, 'inline' => true));
$this->Js->get('#YourForm')->event(
'submit',
$this->Js->request(
array('action' => 'checkUsername', 'controller' => 'user'),
array(
'update' => '#na',
'data' => $data,
'async' => true,
'dataExpression'=>true,
'method' => 'POST'
)
)
);
echo $this->Js->writeBuffer();
?>
The Function in User Controller
function checkUsername(){
$this->autoRender = false;
$username = $this->User->find('first', array('conditions'=>array('User.username'=>$this->request->data['User']['username'])));
if ( $username == true )
echo 'Username is taken';
else
echo 'Username is not taken';
}
EDIT**
*If you want to use jQuery to do this and not the CakePHP Helper you can use aJax to call an action, then update your element like below*
$('#element').on('click', function() {
$.ajax({
url : '/controller/action',
type: 'POST',
success : function(response){
$('#elementToUpdate').html(response);
}
});
}
});
In your Controller Action you can return the "string" you would like to show in the view
function action(){
$string = 'Show this in the view';
return $string;
}
The above example would be executed when you "Click" an element with an id of "element" then upon "Success" would change element with id of "elementToUpdate" to the String "Show this in the view" Since it was returned from the controller action.