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

Posted by mo ode
mo ode
4,352 Points

The <ul> stored in the variable list has a click event listener that targets each <button> in the list. Complete the cod

The <ul> stored in the variable list has a click event listener that targets each <button> in the list. Complete the code to add a class of highlight to a <p> element that's an immediate previous sibling of the button being clicked. I don't have a clue can you help?

app.js 
var 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>

5 Answers

Muhammad Tahir
Muhammad Tahir
4,113 Points
Muhammad Tahir
Muhammad Tahir
4,113 Points

You'll need to add a class name 'highlight' on each button click. 

className

Each button should add the class to it's immediate previous sibling i.e. p.

previousElementSibling

Here is how the final code should look:

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

list.addEventListener('click', function(e) {
  if (e.target.tagName == 'BUTTON') {
    e.target.previousElementSibling.className = 'highlight';
  }
});
RODRIGO MARTINEZ
RODRIGO MARTINEZ
5,912 Points
RODRIGO MARTINEZ
RODRIGO MARTINEZ
5,912 Points

Thanks a lot Muhammad. I was struggling with this one too.

Berat Sakipi
Berat Sakipi
10,276 Points

Can you please explain why it doesn't work without .target? So e.previousElementSibling.className = 'highlight';

T. Gontarek
T. Gontarek
7,030 Points
T. Gontarek
T. Gontarek
7,030 Points

Nick Huemmer - I think it is short for 'event'.

Henry Blandon
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.a{fill-rule:evenodd;}techdegree seal-36
Henry Blandon
Full Stack JavaScript Techdegree Graduate 21,521 Points
Henry Blandon
.a{fill-rule:evenodd;}techdegree seal-36
Henry Blandon
Full Stack JavaScript Techdegree Graduate 21,521 Points

In this example the event type is -click- and the -e- is just a variable that stores the event(when the user clicks the button), then you can use that variable in the code. because is a variable you can actually name it hamburger if you want, and the code still works, but we give variables meaningful names, in this case is an event so they use -e- for short. here is a link where you can see other mouse event like mouseover, mouseout etc. https://developer.mozilla.org/en-US/docs/Web/Events I hope it helps.

Henry Blandon
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.a{fill-rule:evenodd;}techdegree seal-36
Henry Blandon
Full Stack JavaScript Techdegree Graduate 21,521 Points
Henry Blandon
.a{fill-rule:evenodd;}techdegree seal-36
Henry Blandon
Full Stack JavaScript Techdegree Graduate 21,521 Points

Berat, to explain why it doesn't work without the target. In simple English the target is what someone clicks inside the un-order list which was stored in the variable*list* (they could click the button or the paragraph), but inside the code there is a if statement that tells the function to run only if they click a BUTTON, once the computer determined a button was clicked then continues to assigned the class name "highlight" to the target(button) previous element sibling, in this case is the paragraph. If you omit the target, the function doesn't know what was clicked, therefore, doesn't know who the previous element is. I hope it helps.

Radoslaw Proscewicz
Radoslaw Proscewicz
2,916 Points
Radoslaw Proscewicz
Radoslaw Proscewicz
2,916 Points

Why do we only use an "=" operator to assign class name above? Shouldn't we use "==" for stricter equality, as in e.target.previousElementSibling.className == 'highlight' ?

Karen Bacilio
Karen Bacilio
9,459 Points

My understanding is when you use one '=' operator it means you're changing the value to that. Versus a double '==' means it is a Boolean operator, meaning you are comparing two values.

Ndhokoyo Aaron
Ndhokoyo Aaron
6,589 Points
Ndhokoyo Aaron
Ndhokoyo Aaron
6,589 Points

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

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