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

Why my code is incorrect here? Shouldn't use 'p' to reference paragraph?


var list = document.getElementsByTagName('ul')[0];
let p = document.querySelectorAll ('p');

list.addEventListener('click', function(e) {
  if (e.target.tagName == 'BUTTON') {
    p.previousElementSibling.className = 'highlight'
<!DOCTYPE html>
        <title>JavaScript and the DOM</title>
    <link rel="stylesheet" href="style.css" />
            <h1>Making a Webpage Interactive</h1>
            <p>Things to Learn</p>
                <li><p>Element Selection</p><button>Highlight</button></li>
                <li><p>Event Listening</p><button>Highlight</button></li>
                <li><p>DOM Traversal</p><button>Highlight</button></li>
        <script src="app.js"></script>

1 Answer

Hi Hanwen!

No, you don't need to reference any p tags, since you are using DOM sibling transversal.

This passes:

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

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

Note that the strategy/logic here is to target all the buttons and then add the highlight class to each button's previousElementSibling, which are, in each case, paragraphs.

The reason to learn to do DOM transversal this way is that, in certain cases, some elements are more difficult to target than others. In other words, sometimes it's easier to target an easy-to-target element (because it has an easily identifiable id, for example) and the transverse up or down the DOM structure to find your real intended target, because perhaps that element has no identifying id or class.

It's analogous to calling or texting someone whose phone number you do have to try to get ahold of someone whose number you don't have/can't remember (but the person you did call knows how to get in touch with the real person you need to call/text).

Does that make sense?

I hope that helps.

Stay safe and happy coding!

Hi Peter,

I understood now, Thank you so much for your detailed explanation.