Force JavaScript reload just once a day
<script type="text/javascript" src="http://external.example.com/bookmarklet.js?random"></script>

javascript:javascript:(function(){
var the_time = new Date();
  new_script=document.createElement(&#39;SCRIPT&#39;);
 new_script.type=&#39;text&#47;javascript&#39;;
 new_script.src=&#39;http:&#47;&#47;example.com&#47;js&#47;bookmarklet.js?x=&#39; + the_time.getDate() + the_time.getMonth() + the_time.getFullYear());
  document.getElementsByTagName(&#39;head&#39;)&#91;0&#93;.appendChild(new_script);
})();

<script src="http://external.example.com/bookmarklet.js?<?php echo date('Ymd'); ?>"  type="text/javascript"></script>