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

Jose Medina
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
Jose Medina
Front End Web Development Techdegree Graduate 15,656 Points
Posted by Jose Medina
.a{fill-rule:evenodd;}techdegree seal-36
Jose Medina
Front End Web Development Techdegree Graduate 15,656 Points

How to get the last of the <li> in a <ul>

The task is to assign the class name to every previous <li> The problem is the first line, I can't find a way for the code to pick the last item, instead, it goes to null

So my code in JS is 

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

list.addEventListener('click', function(e) {
  if (e.target.tagName == 'BUTTON') {
    let li = e.target.parentNode;
    if (li.previousElementSibling == null) {
      let lastLi = li.querySelector('li')[3];
      lastLi.className = 'highlight';
    } else {
      let nextLi = li.previousElementSibling;
      nextLi.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 id=''><p>DOM Traversal</p><button>Highlight</button></li>
            </ul>
        </section>
        <script src="app.js"></script>
    </body>
</html>

2 Answers

Steven Parker
Steven Parker
229,786 Points
Steven Parker
Steven Parker
229,786 Points

You're working to hard.

This challenge would normally be done by adding a single line of code. Rethink it a little bit, I see you're already using all the properties that you would need to solve it (along with a lot extra).

Hint: You won't need to reference the parent (li) element at all.

Jose Medina
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
Jose Medina
Front End Web Development Techdegree Graduate 15,656 Points
Jose Medina
.a{fill-rule:evenodd;}techdegree seal-36
Jose Medina
Front End Web Development Techdegree Graduate 15,656 Points

Thank you for your reply! So I tried this but hit the same wall. Suggestions? 

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

list.addEventListener('click', function(e) {
  if (e.target.tagName == 'BUTTON') {
    list.querySelector('p').previousElementSibling.className = 'highlight';
  }
});
Steven Parker
Steven Parker
229,786 Points
Steven Parker
Steven Parker
229,786 Points

You won't refer to list inside your event handler. But you will likely want to perform traversal referencing e.target.