Add event listener

---

examples/dom/add_event_listener.html

<button id="btn">Click me</button>

<div id="display"></div>

<script src="add_event_listener.js"></script>

examples/dom/add_event_listener.js

"use strict";

function clicked() {
    document.getElementById('display').innerHTML = 'Hello World';
}

document.getElementById('btn').addEventListener('click', clicked);