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JavaScript JavaScript and the DOM (Retiring) Responding to User Interaction Event Delegation

Posted by Maksym Novikov
Maksym Novikov
4,580 Points

Didn't get the task

I solved this task but I didn't get why don't we have to remove [0] in the first line. The requirement is to make any inputs change their's background, so why we have to keep [0]?

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>JavaScript is an exciting language that you can use to power web servers, create desktop programs, and even control robots. But JavaScript got its start in the browser way back in 1995.</p>
            <hr>
            <p>Things to Learn</p>
            <ul>
                <li>Item One: <input type="text"></li>
                <li>Item Two: <input type="text"></li>
                <li>Item Three: <input type="text"></li>
                <li>Item Four: <input type="text"></li>
            </ul>
            <button>Save</button>
        </section>
        <script src="app.js"></script>
    </body>
</html>
app.js 
let section = document.getElementsByTagName('section')[0];

section.addEventListener('click', (e) => {
  if ( e.target.tagName === 'INPUT' ) {
    e.target.style.backgroundColor = 'rgb(255, 255, 0)';    
  }
});

2 Answers

Steven Parker
Steven Parker
231,236 Points
Steven Parker
Steven Parker
231,236 Points

The getElementsByTagName function returns an HTMLcollection, but you can only attach an event listener to an element. The [0] index selects the first element from the collection (which happens to be the only one on this page).

Maksym Novikov
Maksym Novikov
4,580 Points

Thank u

Alexander Solberg
Alexander Solberg
14,350 Points
Alexander Solberg
Alexander Solberg
14,350 Points

It's because when selecting with .getElementsByTagName(), a HTMLCollection is created.

Even though you are only selecting one element(the <section> tag), you are doing it with .getElements, so in plural form, meaning you are retrieving an array-like value which needs an index to reference specific elements.

I found a treehouse post that might be worth a read: https://teamtreehouse.com/community/understanding-the-difference-between-an-htmlcollection-and-a-nodelist

Maksym Novikov
Maksym Novikov
4,580 Points

Tha a lot