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

Michael Lawinger
Michael Lawinger
33,581 Points
Posted by Michael Lawinger
Michael Lawinger
33,581 Points

Delegating Click Event

The challenge question I'm struggling with is: A delegated click event listener has been attached to the selected ul element, which is stored in the variable list. The handler is targeting each button in the list. When any one of the buttons is clicked, a class of highlight should be added to the paragraph element immediately preceding that button inside the parent list item element. Add the code to create this behavior on line 5.

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

list.addEventListener('click', function(e) {
  if (e.target.tagName == 'BUTTON') {
    let list = event.target.addClass('hightlight');
  }
});
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

Ahmed Magdy
Ahmed Magdy
Courses Plus Student 564 Points

You should apply the highlight class to the previous element sibling of the button tag. like this

const list = document.getElementsByTagName('ul')[0];
list.addEventListener('click', function(e) { 
var el = e.target; //Grabs the button tag when clicked. 
if (el.tagName == 'BUTTON') { 
el.previousElementSibling.className = 'highlight'  /*Applies the class "highlight" to the previous element of button which is the p tag.*/
} });
Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

You have the right idea about adding the class.

But .addClass is a jQuery method. For this course we're using plain JavaScript, so you might use .classList.add instead. And highlight should be spelled with: only one "t"). Also you named your parameter "e", not "event".

But back to adding the class, the test has already determined that the event target is a button. But instead of applying the class to the button, you want to apply it to the paragraph that comes before the button. Remember that the property of an element that refers to the one before it is called previousElementSibling.

I'll bet you can get it now without an explicit spoiler.

Michael Lawinger
Michael Lawinger
33,581 Points
Michael Lawinger
Michael Lawinger
33,581 Points

Thanks guys I was struggling on the very last question of the course.