---
description: A new compatibility flag aligns event dispatch exception handling with the DOM specification.
title: Spec-compliant dispatchEvent() exception handling
image: https://developers.cloudflare.com/changelog/post/2026-08-19-spec-compliant-dispatch-exceptions/og.png?v=95e9857bd850db68
---

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August 19, 2026

## Spec-compliant dispatchEvent() exception handling

[Workers](https://developers.cloudflare.com/workers/)

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A new compatibility flag, `spec_compliant_dispatch_exceptions`, aligns the Workers runtime's event dispatch behavior with the [DOM specification ↗︎](https://dom.spec.whatwg.org/#dispatching-events). This flag becomes the default for all Workers with a compatibility date of `2026-09-15` or later.

Previously, when an event listener threw an exception during `dispatchEvent()`, the runtime propagated the exception immediately and skipped all remaining listeners for that event. The spec instead requires that listener exceptions are reported (via the global `error` event and the console) without interrupting the dispatch — remaining listeners still run.

This change affects the JS-visible `dispatchEvent()`, `AbortSignal` abort dispatch, and runtime-fired events on `WebSocket`, `EventSource`, and `MessagePort`. Top-level event delivery for legacy Service Worker syntax entry points (such as `addEventListener("fetch", ...)`) is not affected.

To opt in before the default date, add `spec_compliant_dispatch_exceptions` to your `compatibility_flags`. To preserve the old behavior after the default date, use `no_spec_compliant_dispatch_exceptions`.

For more details, refer to the [compatibility flags documentation](https://developers.cloudflare.com/workers/configuration/compatibility-flags/).

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