Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

JavaScript JavaScript and the DOM (Retiring) Traversing the DOM Sibling Traversal

what does the (e) in function(e) means? What does the event in function mean? do we use the (e) letter every time?

Thanks

app.js
var list = document.getElementsByTagName('ul')[0];

list.addEventListener('click', function(e) {
  if (e.target.tagName == 'BUTTON') {
    e.target.previousElementSibling.className = 'highlight';
  }
});
index.html
<!DOCTYPE html>
<html>
    <head>
        <title>JavaScript and the DOM</title>
    </head>
    <link rel="stylesheet" href="style.css" />
    <body>
        <section>
            <h1>Making a Webpage Interactive</h1>
            <p>Things to Learn</p>
            <ul>
                <li><p>Element Selection</p><button>Highlight</button></li>
                <li><p>Events</p><button>Highlight</button></li>
                <li><p>Event Listening</p><button>Highlight</button></li>
                <li><p>DOM Traversal</p><button>Highlight</button></li>
            </ul>
        </section>
        <script src="app.js"></script>
    </body>
</html>

3 Answers

Hi Hanwen!

The 'e' is a browser window event object that you can add event listeners to harness and corresponding code to handle/respond to (such as clicking on an element).

More info:

https://developer.mozilla.org/en-US/docs/Learn/JavaScript/Building_blocks/Events

https://developer.mozilla.org/en-US/docs/Web/Events

https://www.smashingmagazine.com/2013/11/an-introduction-to-dom-events/

I hope that helps.

Stay safe and happy coding!

Thank you Peter

The 'e' means event in function, but I could be wrong.

What does the event in function means? do we use the (e) letter everytime?

By the way, you can actually use any variable name to reference the event object, but traditionally and logically most often 'event' or 'e' (short/abbreviation for 'event') is used.

More info:

https://developer.mozilla.org/en-US/docs/Learn/JavaScript/Building_blocks/Events

I hope that helps.

Stay safe and happy coding!

Thanks for the information!!!