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

Iulia Suviteanu
Iulia Suviteanu
822 Points

Hi. I don't know the answer fot this topic. Can you help me, please?

I don't understand why this is not working.

app.js
const list = document.getElementsByTagName('ul')[0];
const button = document.getElementsByTagName('button');
list.addEventListener('click', function(e) {
  if (e.target.tagName == 'BUTTON') {
        let li = event.target.parentNode;
        let prevP = button.previousElementSibling;
        if (prevP) {
          li.insertBefore(button, prevP);
        }
  }
});
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>
Iulia Suviteanu
Iulia Suviteanu
822 Points

this is the problem: 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.

3 Answers

Iulia Suviteanu
Iulia Suviteanu
822 Points

const list = document.getElementsByTagName('ul')[0]; const button = document.getElementsByTagName('button'); list.addEventListener('click', function(e) { if (e.target.tagName == 'BUTTON') { let prg = event.target.previousElementSibling; if (prg) { prg.addClass = 'highlight'; } } });

I tried this...but it's not working

addClass is a JQuery method which we aren't using here but would be:

prg.addClass('highlight')

instead of:

prg.addClass = 'highlight'

Since we aren't using JQuery try

prg.className = 'highlight'

Think of the button's previous sibling and add the style there using previousSiblingElement().