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JavaScript Callback Functions in JavaScript Callbacks and the DOM Callbacks with DOM Elements

Posted by John Locken
John Locken
16,540 Points

Attempting to streamline final task in Callback Functions in JavaScript

I'm looking to streamline the code to the final task in the Callback Functions course. I understand the easy way to do it, which is to create an addEventListener for each button. I am looking to see if there is a way to do it with a single Event Listener. I tried adding the class "button" to all buttons, then creating a const = event => getElementByClass , but I am getting an error which I will paste below. Is this possible, and if so, what am I missing?

app.js 
const btn1 = document.getElementById("button1");
const btn2 = document.getElementById("button2");
const btn3 = document.getElementById("button3");
const butClick = event => {event.target.className = 'button'}

function spinElement(event) {
  //Applies spinning animation to button element
  event.target.className = "spin";
}

butClick.addEventListener('click', spinElement)
index.html 
<!DOCTYPE html>
<html lang="en">
    <head>
        <title></title>
        <link rel='stylesheet' href='styles.css'>
    </head>
    <body>
        <section >
            <button class = 'button' id='button1'>Button 1</button>
            <button class = 'button' id='button2'>Button 2</button>
            <button class = 'button' id='button3'>Button 3</button>
        </section>
        <script src='app.js'></script>
    </body>
</html>
John Locken
John Locken
16,540 Points

Bummer: There was an error with your code: TypeError: 'undefined' is not a function (evaluating 'butClick.addEventListener('click', spinElement)')

Cheo R
Cheo R
37,150 Points
Cheo R
Cheo R
37,150 Points

I think because you're using a fat arrow function, addEventLIstener uses the this referring to window. So essentially, you're trying to attach addEventListener to window, not butClick.

1 Answer

Camilo Lucero
Camilo Lucero
27,692 Points
Camilo Lucero
Camilo Lucero
27,692 Points

Create the event listener over the parent of the buttons and make a condition so the function only executes if the clicked element (event.target) is a button:

const buttonsContainer = document.getElementById("buttons");

function spinElement(event) {
  if (event.target.tagName === "BUTTON") {
    event.target.className = "spin";
  }
}

buttonsContainer.addEventListener("click", spinElement);

<!DOCTYPE html>
<html lang="en">
    <head>
        <title></title>
        <link rel='stylesheet' href='styles.css'>
    </head>
    <body>
        <section id='buttons'>
            <button id='button1'>Button 1</button>
            <button id='button2'>Button 2</button>
            <button id='button3'>Button 3</button>
        </section>
        <script src='app.js'></script>
    </body>
</html>

Even though this works for your goal (preview the HTML to test it), the challenge will show you an error when submitting this answer. Sometimes challenges are designed to check for a specific answer, and don't expect you to get creative :)