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

Piotr Manczak
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Piotr Manczak
Front End Web Development Techdegree Graduate 29,363 Points
Posted by Piotr Manczak
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Piotr Manczak
Front End Web Development Techdegree Graduate 29,363 Points

I am not sure if I know what they want from me. Do they want me to change class name of the <p> to highlight?

If yes, which method of targeting a <button> element would be best?

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

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

4 Answers

Louise St. Germain
Louise St. Germain
19,424 Points
Louise St. Germain
Louise St. Germain
19,424 Points

Yes, the simple solution works! :-)

In fact, you could simplify two lines into one, like this:

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

list.addEventListener('click', function(e) {
  if (e.target.tagName == 'BUTTON') {
     // Combine the two lines into one step
     e.target.previousElementSibling.className = 'highlight';    
  }
});
Louise St. Germain
Louise St. Germain
19,424 Points
Louise St. Germain
Louise St. Germain
19,424 Points

Hi Piotr,

Yes, they are looking for you to change the class name of the p to "highlight", but only for the p that is right before the button that got clicked.

You have the right idea to use previousElementSibling to find the p, but you will need to do that inside the event listener. If you do it before (as in your code above), it selects a p before you've even clicked a button, which is not what we want.

So, your code should be something like:

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

list.addEventListener('click', function(e) {
  if (e.target.tagName == 'BUTTON') {
     // TODO: Find e.target's previousElementSibling (which should be a p)
     // TODO: Set that element's class name to "highlight".
  }
});

I hope this helps to clarify!

Piotr Manczak
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
Piotr Manczak
Front End Web Development Techdegree Graduate 29,363 Points
Piotr Manczak
.a{fill-rule:evenodd;}techdegree seal-36
Piotr Manczak
Front End Web Development Techdegree Graduate 29,363 Points

What do you think about this:

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

list.addEventListener('click', function(e) {
  if (e.target.tagName == 'BUTTON') {
    var li = e.target.parentNode;
    var button = document.getElementsByTagName('button');
    var p = button.previousElementSibiling;
    p.className = 'highlight';
  }
});

MOD: Just reformatted so the code is easier to read!