Ajax-example.php

<?php
/*
The Ajax examples at https://developer.wordpress.org/plugins/javascript/ajax/
and the subsequent PHP page are incomplete, which prevents them from working
correctly. My full version of the examples which have worked for me.
*/

// The HTML, added to a custom HTML block in a post
?>
<form id="radioform">
<table>
<tbody>
<tr>
<td><input class="pref" checked="checked" name="book" type="radio" value="Sycamore Row">Sycamore Row</td>
<td>John Grisham</td>
</tr>
<tr>
<td><input class="pref" name="book" type="radio" value="Dark Witch">Dark Witch</td>
<td>Nora Roberts</td>
</tr>
</tbody>
</table>
</form>

<?php
/*
 The relevant PHP in a plugin that I created. Does not include the comment header
 required for any plugin's main file.

    Enqueue required scripts and prepare needed data
    Script invoked by changing book selection in the above form
*/
function my_enqueue($hook) {
    wp_enqueue_script( 'ajax-script',
        plugins_url( '/js/my-jquery.js', __FILE__ ),
        array('jquery')
    );
    $author_nonce = wp_create_nonce( 'title_example' );
    wp_localize_script( 'ajax-script', 'my_ajax_object', array(
        'ajax_url' => admin_url( 'admin-ajax.php?my-test=hello' ),
        'nonce' => $author_nonce,
        'post_id' => get_queried_object_id(),
    ));
}
add_action('wp_enqueue_scripts', 'my_enqueue');


/* Handle an AJAX request */
function my_ajax_handler() {
    check_ajax_referer( 'title_example' );
    update_user_meta( get_current_user_id(), 'title_preference', $_POST['title'] );
    $args = array(
        'tag' => $_POST['title'],
    );
    $the_query = new WP_Query( $args );

    // appends (0) to the passed title as the query normally fails to find anything
    echo $_POST['title'].' ('.$the_query->post_count.') ';
    wp_die();       // All ajax handlers should die when finished
}
add_action( 'wp_ajax_my_tag_count', 'my_ajax_handler' );
add_action( 'wp_ajax_no_priv_my_tag_count', 'my_ajax_handler' );


// Content of my plugin's /js/my-jquery.js file
?>
jQuery(document).ready(function($) {           //noConflict wrapper

    $(".pref").change(function() {             //event

        var this2 = this;                      //use in callback
        $.post(my_ajax_object.ajax_url, {         //POST request
           _ajax_nonce: my_ajax_object.nonce,     //nonce
            action: "my_tag_count",            //action
            title: this.value                  //data
        }, function(data) {                    //callback
            this2.nextSibling.remove();        //remove current title
            $(this2).after(data);              //insert server response
        });
    });
});