User:GhostInTheMachine/SubPages.js Source: en.wikipedia.org/wiki/User:GhostInTheMachine/SubPages.js

if(mw.config.get('wgNamespaceNumber')) {
  mw.util.addPortletLink(
    'p-namespaces',
    mw.util.getUrl('Special:PrefixIndex/') + mw.config.get('wgPageName') + '/',
    'Subpages',
    'ca-subpages',
    'List sub-pages'
  );
}