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

Julian Laub
Julian Laub
1,982 Points
Posted by Julian Laub
Julian Laub
1,982 Points

Where is my mistake?

The task is to add the class: highlight to the paragraph above the selected element, as I understood.

I get returned null, which would happen if the button selected is the first one and the previousSiblingElement is not existing. So I could insert a new html li and p element. But that is not what was asked.

So I don't see what I could change.

Thanks

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

list.addEventListener('click', function(e) {
  if (e.target.tagName == 'BUTTON') {
    let li = e.target.parentNode;
    let prevli = li.previousElementSibling;
   prevli.p.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>

3 Answers

Steven Parker
Steven Parker
231,008 Points
Steven Parker
Steven Parker
231,008 Points

You got pretty close.

You just went too far back in the ancestry. The paragraph element is the sibling of the button itself, not the button's parent li element.

    let parg = e.target.previousElementSibling;
    parg.className='highlight';
Julian Laub
Julian Laub
1,982 Points
Julian Laub
Julian Laub
1,982 Points

Thanks. I see, I modeled what the interpreter would be doing.

Julian Laub
Julian Laub
1,982 Points
Julian Laub
Julian Laub
1,982 Points

Ok. Now I got it, yeah I thought it should be the paragraph of the list before.