title: improving yslow score on external js file with expiry date that you have no control of
body: <p>I am getting a grade C on my YSlow because I have the following files not having an expiry date:</p>
  
  <p><img src="https://i.stack.imgur.com/9ZkWJ.png" alt="enter image description here"></p>
  
  <p>If you can't see what are those files, mostly those are facebook sdks js, twitter share widget js, live chat javascript widget, crazy egg javascript widget, and google plus javascript sdk. So I have no control of how they set the expiry date for these files. So then I am stuck, what should I do to resolve this issue?</p>