hasDevTools.js

const hasDevTools = (function () {
  const ping = new Image();
  let devToolsOpened;

  Object.defineProperty(ping, 'id', {
    get() { devToolsOpened = true; }
  });

  return function hasDevTools () {
    devToolsOpened = false;
    console.log('.%c', ping);
    return devToolsOpened;
  };
})();