Attaching JS to every page's footer in with WordPress best practices.

attach-js.php

<?php
/**
 * All code should live in functions.php of the active theme
 */
 
 function attach_js() { ?>
  <script type="text/javascript">
    document.write('ALL MY JS CAN GO IN BETWEEN THESE SCRIPT TAGS'); //Test script only, not required
  </script>
 <?php }
 
 // Adds an action the footer of every page. In this case, just add some JS
 add_action('wp_footer', 'attach_js');