WordPress AJAX call throws undefined index error in custom plugin

Other Questions Wordpress
1

I’m working on a custom WordPress plugin and trying to implement AJAX functionality. However, I keep running into an undefined index error whenever I make the AJAX request.

The error message I’m getting is:

Notice: Undefined index: data_value

Here’s my JavaScript code that sends the AJAX request:

add_action('admin_footer', 'send_ajax_request');

function send_ajax_request() {
    ?>
    <script type="text/javascript">
    jQuery(document).ready(function($) {
        var requestData = {
            'action': 'handle_custom_request',
            'data_value': 5678
        };
        
        $.post(ajaxurl, requestData, function(result) {
            console.log('Server response: ' + result);
        });
    });
    </script>
    <?php
}

And here’s my PHP callback function:

add_action('wp_ajax_handle_custom_request', 'process_ajax_data');

function process_ajax_data() {
    global $wpdb;
    
    $user_input = intval($_POST['data_value']);
    $calculated_result = $user_input + 25;
    
    echo $calculated_result;
    wp_die();
}

I can’t figure out why the index is showing as undefined. The AJAX call seems to be structured correctly but something isn’t working right. Any ideas what might be causing this issue?

2

Your AJAX request isn’t reaching the callback function. I had the same issue with a membership plugin last year. The problem was my script wasn’t enqueued with the right dependencies. Don’t hook your JavaScript to admin_footer - use a proper enqueue function instead. Also, localize the script to pass ajaxurl correctly. Sometimes ajaxurl isn’t defined in the scope you’re using it. Add error logging at the start of process_ajax_data() to see if your callback’s even firing. WordPress will silently fail to register AJAX actions if there are PHP errors somewhere else in your plugin.

3

make sure you have the right hook for loading your scripts. sometimes, it helps to use wp_enqueue_scripts for front end stuff. also, check out your AJAX URL – if it’s not set correctly, it’ll throw that undefined index error. good luck!

4

This is WordPress’s AJAX nonce security system blocking your request. I ran into the exact same issue when I started with WordPress AJAX. Without proper nonce verification, WordPress strips the POST data before it hits your callback function - that’s why you’re getting the undefined index error. Here’s what you need to do: generate a nonce in your PHP using wp_create_nonce('your_nonce_name') when localizing your script, then verify it in your callback with wp_verify_nonce(). Don’t forget to register the AJAX action for both logged-in and non-logged-in users by adding the wp_ajax_nopriv_ hook too. Most people miss this security step, but it’s crucial for WordPress AJAX to work.