require_once('Services/JSON.php');

$json = new Services_JSON();
$obj = array(
    'id'   => array(
       'foo',
       'bar',
       array('aa' => 'bb')
       ),
       'foobar' => $string,
       'a'   => 123 ,
       'b'   => true
);
$js = $json->encode($obj);
echo $js;