CustomEvent.detail

// create custom events
const catFound = new CustomEvent('animalfound', {
  detail: {
    name: 'cat'
  }
});
const dogFound = new CustomEvent('animalfound', {
  detail: {
    name: 'dog'
  }
});

// add an appropriate event listener
obj.addEventListener('animalfound', (e) => console.log(e.detail.name));

// dispatch the events
obj.dispatchEvent(catFound);
obj.dispatchEvent(dogFound);

// "cat" and "dog" logged in the console