what’s the way to access variables from serializeArray

You should be getting the data from the $_POST server variable, not the $_REQUEST eg.

(isset($_POST)) {
    $postData = $_POST['post_data'];
}

$_REQUEST doesn’t force you to figure out if the variable came from GET, POST, COOKIES, etc. It’s useful for debugging scripts or when the variable might come form one of several sources. For instance you might have form information coming from a form (POST) or form a link (GET).

There are security considerations, however, since $_REQUEST captures data from several sources including cookies, so there’s a potential for misbehavior if someone gets clever and you’re not careful.

In order to use the posted JSON (JavaScript Object Notation) data in PHP you can use json_decode() eg.

$postData = json_decode( $_POST['post_data'] );

Then, for example, to access the variables you would need to use:

_wpnonce – $postData[0]->value

_wp_http_referer – $postData[1]->value

user_ID – $postData[2]->value

Or, if you wanted to return a tidier array that is more readable, you could use this on the json_decoded $postData:

$tidy_array = array();

foreach ( $postData as $object ){
    $tidy_array[$object->name] = $object->value;
}

Then you could access the data like so:

$tidy_array['_wpnonce']

$tidy_array['_wp_http_referer]

$tidy_array['user_ID']