title: How to check if service-worker exist in given URL?
body: <p>Can I distinguish given external web sites have 'service-worker' or not?</p>
  
  <p>My best guess is:</p>
  
  <ol>
  <li>retrieve all the js files from given URL </li>
  <li>search for string 'sw.js'</li>
  </ol>
  
  <p>(i am unsure how to do this as well)</p>
  
  <p>Given data would be like this:</p>
  
  <pre><code>const sitesToCheck = {
      'www.site1.com',
      'www.site2.com',
      'www.site3.com',
  }
  </code></pre>