HTML transitionend DOM Event: Reference and Examples

When someone interacts with a webpage, the browser sends events to the relevant JavaScript code. The transitionend event happens when a CSS transition finishes.

When transitionend happens

A CSS transition finishes.

You can listen for it using addEventListener(). That keeps event handling separate from HTML attributes such as onclick and works well with modern code organization.

A small working example

<style>
    .animated-box { opacity: 1; transition: opacity 1s; }
    .animated-box:hover { opacity: .3; }
</style>
<div id="demo-target" class="animated-box">Animate this box with CSS</div>
<p id="event-status" role="status">Waiting for transitionend...</p>
<script>
    const eventTarget = document.getElementById("demo-target");
    const eventStatus = document.getElementById("event-status");

    if (eventTarget) {
        eventTarget.addEventListener("transitionend", (eventDetails) => {
            eventStatus.textContent = "transitionend event received";
            console.log(eventDetails.type, eventDetails.target);
        });
    }
</script>

Reading the code

The browser listens for transitionend on the relevant target. When the event occurs, the callback receives eventDetails, updates the status message and logs the event name and target in Developer Tools.

Change a CSS property with a transition and wait until it ends.

The CSS rule above makes the animation or transition possible. Without a real animated property, a listener alone cannot make these events fire.

Try it in your browser

Open the page, show the Console panel, and follow this test: Change a CSS property with a transition and wait until it ends. Then change one thing in the example and observe whether the event still fires.

Common Beginner Mistakes

• Expecting transitionend to fire without its required user action or browser condition.
• Change a CSS property with a transition and wait until it ends.
• Adding repeated event listeners without considering cleanup or unwanted side effects.

Key Takeaways

• transitionend reports a CSS transition finishes.
• addEventListener("transitionend", ...) listens for the event on the appropriate target.
• Change a CSS property with a transition and wait until it ends.