example.php

<?php

// Assume this is part of a larger plugin project

// Enqueue our AJAX script
// Tell WordPress to make sure jQuery is also loaded as part of our dependency array
wp_enqueue_script( 'ajax-script', plugins_url( '/js/test.js', __FILE__ ), array('jquery') );

// Add 'wp_ajax' tied to the "example_function" action
add_action( 'wp_ajax_example_function', 'example_function_callback' );

// Callback function for the wp_ajax_example_function action
function example_function_callback() {

   // Echo back the some_value passed to it
   echo $_POST["some_value"];

   // Die gracefully to guarantee proper return response
   wp_die(); 
}

?>