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

Whitney Barber
Whitney Barber
9,453 Points
Posted by Whitney Barber
Whitney Barber
9,453 Points

How to add a class to the previous sibling element?

I've tried employing the className property but this returned an error of object undefined. Please assist and thanks!

app.js 
const list = document.getElementsByTagName('ul')[0];
const button = document.getElementsByTagName('button');
list.addEventListener('click', function(e) {
  if (e.target.tagName == 'BUTTON') {
    let p = button.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

Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

:point_right: You're close, but have a few issues yet. Here's some hints:

  • there's no button variable
  • the element you want the sibling of is the event target (e.target)
  • the class name the challenge asked for is "highlight" (with lower-case "l")
  • there's no need to create or set the "p" variable
Whitney Barber
Whitney Barber
9,453 Points
Whitney Barber
Whitney Barber
9,453 Points

Thank you for the helpful hints, I got it!

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

list.addEventListener('click', function(e) { if (e.target.tagName == 'BUTTON') { e.target.previousElementSibling.className = 'highlight'; } });