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

SAMUEL LAWRENCE
PLUS
SAMUEL LAWRENCE
Courses Plus Student 8,447 Points
Posted by SAMUEL LAWRENCE
SAMUEL LAWRENCE
Courses Plus Student 8,447 Points

Code challenge, need help. Sibling traversal.

A delegated click event listener has been attached to the selected ul element, which is stored in the variable list. The handler is targeting each button in the list. When any one of the buttons is clicked, a class of highlight should be added to the paragraph element immediately preceding that button inside the parent list item element. Add the code to create this behavior on line 5.

I don't really understand the question. Should we be using previousElementSibling or nextElementSibling? I'm not sure because both the button and the paragraph elements are children of the li element.

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

list.addEventListener('click', function(e) {
  if (e.target.tagName == 'BUTTON') {

  }
});
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

silvercoder
silvercoder
11,113 Points

Hi, so the button and p elements are both siblings, they exist on the same level in the dom tree so you should use a sibling selector. The p element is before the button element so you should use the previous element sibling selector.

My solution:

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

Hope this helps.

SAMUEL LAWRENCE
SAMUEL LAWRENCE
Courses Plus Student 8,447 Points
SAMUEL LAWRENCE
SAMUEL LAWRENCE
Courses Plus Student 8,447 Points

Hi silvercoder thanks for the reply. My solution was similar to yours although I referenced a lot of unnecessary elements, but it wasn't working. I kept getting a event not defined error in the console and I couldn't figure out why. So I thought I was misunderstanding the question. It turned out, since Guil Hernandez has been using event keyword all the time, I didn't notice that this time he used e so I kept writing event.target.previousElementSibling that's why it was giving me the console error. I changed that to e after looking at your code and it went through. Thanks a lot.

this is what I did before

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

list.addEventListener('click', function(e) {
  if (e.target.tagName == 'BUTTON') {
    let li = event.target.parentNode;
    let prevEl = event.target.previousElementSibling;
    let ul = li.parentNode;
    prevEl.className = 'highlight';
  }
});

I replaced all the event with e and it worked.