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

David Dehghani
David Dehghani
6,992 Points
Posted by David Dehghani
David Dehghani
6,992 Points

Adding a class to a parent node.

Feel like I selected the parent but not confident with which variables I'm selecting, or even if I'm doing the right thing to them.

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

list.addEventListener('click', function(e) {
  if (e.target.tagName == 'BUTTON') {
  let ul = list.querySelectorAll('p');
  let para = ul.previousElementSibling;
  let sib = para.parentNode.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>

1 Answer

Steven Parker
Steven Parker
231,248 Points
Steven Parker
Steven Parker
231,248 Points

:point_right: You don't need to select the parent for this task.

You only need to select the paragraph element which you know is immediately previous to the button itself. Since the code already filters out only events on buttons, you can condense the handler down to something like this.

    e.target.previousElementSibling.className = "highlight";

By starting with the button being pressed (e.target), we can just go directly to the previous sibling element and set the class.

Now FYI, your original code had assigned an element collection to the variable ul using querySelectorAll, and then applied previousElementSibling to that collection. But previousElementSibling only works on a single element, so the value of para would have remained undefined. Plus, you didn't really want to select an element without knowing if it was the one associated with the pressed button anyway.