MediaWiki:Common.js

Note: After publishing, you may have to bypass your browser's cache to see the changes.

Firefox / Safari: Hold Shift while clicking Reload, or press either Ctrl-F5 or Ctrl-R (⌘-R on a Mac)
Google Chrome: Press Ctrl-Shift-R (⌘-Shift-R on a Mac)
Internet Explorer / Edge: Hold Ctrl while clicking Refresh, or press Ctrl-F5
Opera: Press Ctrl-F5.

/* Any JavaScript here will be loaded for all users on every page load. */
(function () {

  let myElement = document.getElementById('mw-hello-world');
  myElement.innerHTML = '<html>Hello World!!!</html>';

}());

console.log('Test?');