User:GhostInTheMachine/SortWhatLinksHere.js

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.
function SortWhatLinksHere($el) {
  $el.append(
    $el.children().sort( (a,b) => a.innerHTML < b.innerHTML ? -1 : a.innerHTML > b.innerHTML ? 1 : 0 )
  );
  $.each($el.children(), (i,$sub) => SortWhatLinksHere($($sub).find('ul')));
}

$(function(){
  SortWhatLinksHere($('#mw-whatlinkshere-list'));
});