vanilla-custom-events.js

// Import stylesheets
import './style.css';

// Write Javascript code!
const appDiv = document.getElementById('app');
appDiv.innerText = 'App';
// register a event handler named 'highlight'
appDiv.addEventListener('highlight', function(event) {
  appDiv.innerText = 'App highlighted';
});

function highlight(elem) {
  elem.classList.add('highlight');
  var event = document.createEvent('CustomEvent');
  event.initCustomEvent('highlight');
  elem.dispatchEvent(event);
};

appDiv.addEventListener('click', function(event) {
  highlight(event.target);
});