Event handler

We can do something based on the browser events, like when a button is clicked, page is scrolled etc.

Let's create a simple html page: 

<html>
    <head>
        <title>Event Handler</title>
        <style>
            .header {
                background-color: aqua;
            }
        </style>
    </head>

    <body>
        <h1 class="header">Hello Event Handler</h1>
    </body>

    <script>
        const topHeader = document.querySelector(".header");

        function clicked() {
            alert("Top header is clicked!")
        }

        topHeader.onclick = clicked;
    </script>
</html>

Now whenever we click our header, we will see an alert saying, "Top header is clicked". The full list of browser events are available in MDN website.