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

Yi Zhang
Yi Zhang
3,572 Points
Posted by Yi Zhang
Yi Zhang
3,572 Points

adding a class to a previous element sibling

I cannot understand where is the error.

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

list.addEventListener('click', function(e) {
  if (e.target.tagName == 'BUTTON') {
    e.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>

2 Answers

Justin Iezzi
Justin Iezzi
18,199 Points

Hi Yi Zhang,

Looks like you've simply forgotten to add the .target property.

e.target.previousElementSibling.className = "highlight";
Nicholas Vogel
Nicholas Vogel
12,318 Points
Nicholas Vogel
Nicholas Vogel
12,318 Points

It's likely this line

e.previousElementSibling.className = "highlight"

You forgot the semi-colon at the end of "highlight". JS is that picky. You can also always check errors in the javascropt console.

miikis
miikis
44,957 Points

Not true, Nicholas. JavaScript has ASI (Automatic Semicolon Insertion); semicolons are rarely needed. In fact, the only time they're ever required — that I can think of off the top of my head — is before return statements that aren't preceded by a newline and IIFEs (Immediately Invoked Functional Expressions) that have been concatenated together.

Steven Parker
Steven Parker
231,008 Points
Steven Parker
Steven Parker
231,008 Points

You also need semicolons between statements that are on the same one.