Enqueue jQuery library as well as your plugin’s custom JavaScript file by adding it to your plugin.

Add-Javascript-AJAX-Support.php

<?php // used here only for enabling syntax highlighting. Leave this out if it's already included in your plugin file.

// Fires after WordPress has finished loading, but before any headers are sent.
add_action( 'init', 'script_enqueuer' );

function script_enqueuer() {
   
   // Register the JS file with a unique handle, file location, and an array of dependencies
   wp_register_script( "liker_script", plugin_dir_url(__FILE__).'liker_script.js', array('jquery') );
   
   // localize the script to your domain name, so that you can reference the url to admin-ajax.php file easily
   wp_localize_script( 'liker_script', 'myAjax', array( 'ajaxurl' => admin_url( 'admin-ajax.php' )));        
   
   // enqueue jQuery library and the script you registered above
   wp_enqueue_script( 'jquery' );
   wp_enqueue_script( 'liker_script' );
}