How to enable WordPress Heartbeat API

heartbeat-api.js

(function ($) {
    "use strict";
  
    $(document).ready(function () {
        // Sending Data to the Server
        jQuery(document).on('heartbeat-send', function (event, data) {
            // Add additional data to Heartbeat data.
            data.myplugin_customfield = 'some_data';
        });

        // Processing the Response
        jQuery(document).on('heartbeat-tick', function (event, data) {
            // Check for our data, and use it.
            if (!data.myplugin_customfield_hashed) {
                return;
            }
            alert('The hash is ' + data.myplugin_customfield_hashed);
        });
    });

})(jQuery);

heartbeat-api.php

<?php defined('ABSPATH') || die('Cheatin&#8217; uh?'); // Cannot access pages directly.

/**
 * REF: https://developer.wordpress.org/plugins/javascript/heartbeat-api/
 * @author Razon Komar Pal
 */

// enqueue the Heartbeat API JS
add_action('init', 'myplugin_enqueue_heartbeat_init');
function myplugin_enqueue_heartbeat_init()
{
    // enqueue heartbeat.js
    wp_enqueue_script('heartbeat');
}


// Add filter to receive hook, and specify we need 2 parameters.
add_filter('heartbeat_received', 'myplugin_receive_heartbeat', 10, 2);

/**
 * Receive Heartbeat data and respond.
 *
 * Processes data received via a Heartbeat request, and returns additional data to pass back to the front end.
 *
 * @param array $response Heartbeat response data to pass back to front end.
 * @param array $data Data received from the front end (unslashed).
 */
function myplugin_receive_heartbeat($response, $data)
{
    // If we didn't receive our data, don't send any back.
    if (empty($data['myplugin_customfield'])) {
        return $response;
    }

    // Calculate our data and pass it back. For this example, we'll hash it.
    $received_data = $data['myplugin_customfield'];

    $response['myplugin_customfield_hashed'] = sha1($received_data);
    return $response;
}

// Limit Heartbeat interval
add_filter('heartbeat_settings', 'myplugin_heartbeat_interval');
function myplugin_heartbeat_interval($settings)
{
    // ref: https://github.com/WordPress/WordPress/blob/master/wp-includes/js/heartbeat.js
    $settings['interval'] = 30; // Anything between 15-120 // Connect interval (in seconds).
    return $settings;
}