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

Shawn Black
Shawn Black
2,164 Points
Posted by Shawn Black
Shawn Black
2,164 Points

I'm pretty sure I know how to traverse the node, but I don't recall how to add a class

I'm assuming the CSS has a class of "highlight" available but using the previousLi.className = "h1" doesn't result in a change to the <li> text. I can successfully use previousLi.style.backgroundColor = 'yellow', but that's not what the directions state.

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

list.addEventListener('click', function(e) {
  if (e.target.tagName == 'BUTTON') {
    let li = event.target.parentNode;
    let previousLi = li.previousElementSibling;
    if (previousLi){
      previousLi.className = "highlight";
//      previousLi.style.backgroundColor = 'yellow';
    }
  }
});
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

KRIS NIKOLAISEN
KRIS NIKOLAISEN
54,971 Points

Sometimes it helps to move the code to a workspace so you can at least use the console. There you could add log statements to see:

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

list.addEventListener('click', function(e) {
  if (e.target.tagName == 'BUTTON') {
    let li = event.target.parentNode;
    console.log(li)
    let previousLi = li.previousElementSibling;
    console.log(previousLi)
    if (previousLi){
      previousLi.className = "highlight";
//      previousLi.style.backgroundColor = 'yellow';
    }
  }
});

In the above li references the list item. previousLi references the previous list item relative to li. However the instructions are to add a class of highlight to a <p> element that's an immediate previous sibling of the button being clicked. If your code is correct the paragraph text to the left of the button will highlight when the button is clicked (in the challenge preview).

Since e.target refers to the button, the immediate previous sibling is simply e.target.previousElementSibling.

Your syntax for setting the class will work.

Shawn Black
Shawn Black
2,164 Points
Shawn Black
Shawn Black
2,164 Points

So much of the lesson in the "JavaScript and the DOM" had us traversing to the parent element. It just didn't register that this question was working within the li element. I honestly thought I needed to highlight the <p> of the previous <li>. Thanks for your help.

Dmitry Polyakov
Dmitry Polyakov
4,989 Points
Dmitry Polyakov
Dmitry Polyakov
4,989 Points

You don't even need to grab on the li element here. You click on a button and add a class of highlight to its previuosElementSibling, which is a paragraph - <p></p>

Shawn Black
Shawn Black
2,164 Points
Shawn Black
Shawn Black
2,164 Points

Like I just told Kris, so much of the lesson in the "JavaScript and the DOM" had us traversing to the parent element. It just didn't register that this question was working within the li element. I honestly thought I needed to highlight the <p> of the previous <li>. Thanks for your help.