HTML rejectionhandled DOM Event: Reference and Examples

When someone interacts with a webpage, the browser sends events to the relevant JavaScript code. The rejectionhandled event happens when a previously unhandled promise rejection later receives a handler.

When rejectionhandled happens

A previously unhandled promise rejection later receives a handler.

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

<p>Try the relevant browser action described below.</p>
<p id="event-status" role="status">Waiting for rejectionhandled...</p>
<script>
    const eventTarget = window;
    const eventStatus = document.getElementById("event-status");

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

Reading the code

The browser listens for rejectionhandled 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.

Attach a rejection handler after the unhandled-rejection event; avoid relying on this for app flow.

eventDetails.promise references the promise that received a late rejection handler.

Some events need a specific browser condition, another tab or window, or a Web Component to reproduce. Read the trigger steps carefully before deciding that an event handler is not working.

Try it in your browser

Open the page, show the Console panel, and follow this test: Attach a rejection handler after the unhandled-rejection event; avoid relying on this for app flow. Then change one thing in the example and observe whether the event still fires.

Common Beginner Mistakes

• Expecting rejectionhandled to fire without its required user action or browser condition.
• Attach a rejection handler after the unhandled-rejection event; avoid relying on this for app flow.
• Adding repeated event listeners without considering cleanup or unwanted side effects.

Key Takeaways

• rejectionhandled reports a previously unhandled promise rejection later receives a handler.
• addEventListener("rejectionhandled", ...) listens for the event on the appropriate target.
• Attach a rejection handler after the unhandled-rejection event; avoid relying on this for app flow.