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JavaScript JavaScript and the DOM (Retiring) Traversing the DOM Sibling Traversal

Jose Medina
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.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
230,248 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

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
230,248 Points

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