Note: After saving, you have to bypass your browser's cache to see the changes. Google Chrome, Firefox, Microsoft Edge and Safari: Hold down the ⇧ Shift key and click the Reload toolbar button. For details and instructions about other browsers, see Wikipedia:Bypass your cache.
// [[user:js/watchlist]]
if (mw.config.get('wgCanonicalSpecialPageName') == 'Watchlist') 
  importScript('user:js/watchlist.js');