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

Posted by Hanwen Zhang
Hanwen Zhang
20,084 Points

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

Peter Vann
Peter Vann
36,425 Points

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!

Hanwen Zhang
Hanwen Zhang
20,084 Points

Thank you Peter

Roxanne Reyes
Roxanne Reyes
9,006 Points
Roxanne Reyes
Roxanne Reyes
9,006 Points

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

Hanwen Zhang
Hanwen Zhang
20,084 Points

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

Peter Vann
Peter Vann
36,425 Points
Peter Vann
Peter Vann
36,425 Points

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!

Hanwen Zhang
Hanwen Zhang
20,084 Points

Thanks for the information!!!