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Use a React Error Boundary to recover a specific part of the interface when a descendant fails during rendering. Use browser global handlers to report certain uncaught JavaScript errors and unhandled Promise rejections. They cover different situations: a global handler does not provide a React fallback, and a boundary does not catch every JavaScript failure.
How the two mechanisms differ
| Failure or task | React Error Boundary | Browser global handler |
|---|---|---|
| A descendant throws while React renders | Yes. The boundary can show fallback UI and report the error through componentDidCatch. |
React says a boundary-caught error bubbles to window in development, but not in production. It is not a dependable production reporting path for errors a boundary handles. React Component reference |
| An event handler throws synchronously | No. Handle the failure in the handler or its action flow. | If it escapes uncaught, it can trigger the browser error event. That reports the exception; it does not replace the affected React UI. MDN: Window error event |
A setTimeout or requestAnimationFrame callback throws |
Generally no; these callbacks run outside the ordinary render handling. | An uncaught synchronous exception can reach the global error event. MDN: Window error event |
| A Promise rejects without a rejection handler | Generally no, unless surfaced through a React-supported path such as a rejected Promise read with use(promise). |
The relevant event is unhandledrejection. Some cross-origin rejections do not fire it. MDN: Window unhandledrejection event |
| An image, script, or other resource fails to load | Not an ordinary descendant-rendering failure. | The error event can be dispatched on the failed element, so a listener on window is not a universal resource-failure detector. MDN: Window error event |
| The boundary itself throws | No. A boundary does not catch errors thrown by itself. | A resulting uncaught synchronous exception may reach the global handler, depending on how it escapes. React Component reference |
| Server-side rendering fails | Ordinary Error Boundary guarantees do not cover server-side rendering. Streaming Suspense has separate server behavior. | Browser window handlers do not handle server execution; server-runtime error handling is separate. React Component reference |
What a React Error Boundary catches—and what it does not
An Error Boundary is a React component that handles errors thrown by its descendant components while React renders them. It can switch the affected part of the tree to fallback UI instead of leaving that part of the page in its failed state. This makes boundaries a recovery tool scoped to the interface.
React documents several exclusions: event handlers, server-side rendering, errors thrown by the boundary itself, and most asynchronous callbacks. An error in a click handler or timer therefore needs handling in that handler or callback rather than reliance on a nearby boundary. React Component reference
Two React-supported paths for errors and rejections
There are specific cases that reach a boundary beyond an ordinary render-time throw. React documents that errors in the function passed to useTransition‘s startTransition can reach an Error Boundary. React useTransition reference
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A rejected Promise read using React’s use(promise) also reaches the nearest Error Boundary. The Promise must be cached so the same Promise is read across renders; creating a new Promise each render can cause problems. React use reference
Where to place boundaries
Put a boundary where it makes sense to replace a failed area with fallback UI—for example, around a conversation list or an individual message. A boundary around the entire app may offer a final fallback, but more local boundaries let unaffected parts of the interface remain available. Wrapping every component mechanically is not necessary.
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What browser global handlers observe
Browser global handling addresses errors that escape to the global execution scope; it does not create a React fallback or repair a failed component tree. The two relevant browser events describe different kinds of failure:
errorreports synchronous script errors that reach the global scope. Resource-loading errors can instead be dispatched on the failed element.unhandledrejectionreports a Promise rejection for which no rejection handler was attached. Some cross-origin rejections do not trigger the event.
These events are not interchangeable. A Promise rejection is not a synchronous script exception, so listen for unhandledrejection when reporting unhandled Promise failures. MDN: Window error event MDN: Window unhandledrejection event
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addEventListener("error", ...) versus window.onerror
With window.addEventListener("error", callback), the callback receives an event object. The historical window.onerror property instead receives five arguments. MDN notes an unusual rule for that property: returning true suppresses the browser’s default console report, but does not resume the failed script. Avoid suppressing the default report unless you deliberately want to take over that behavior. MDN: Window error event
For unhandledrejection, calling preventDefault() suppresses the default reporting behavior. Do so only if your code intentionally assumes responsibility for reporting the rejection. MDN: Window unhandledrejection event
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How to report boundary errors in React
The documented class-boundary pattern uses static getDerivedStateFromError to select fallback state. Use componentDidCatch(error, info) to log details; info.componentStack contains the component stack.
React does not currently offer a direct function-component equivalent for componentDidCatch. Its reference points to the react-error-boundary package as an alternative for function-component-oriented use. React Component reference
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React 19 root callbacks
React 19 adds onCaughtError and onUncaughtError root options alongside onRecoverableError. The first is for errors React catches in an Error Boundary; the second is for errors not caught by a boundary. These callbacks depend on configuring the React root, and provide reporting hooks rather than replacing a boundary’s local fallback UI. React 19 release notes
Quick Recap
Choose the handling point that matches the failure
- A component fails while rendering: put an Error Boundary around the part of the UI that should recover, and report it through
componentDidCatchor a React 19 root callback. - An event handler or callback fails: handle errors where the action runs. A global
errorlistener can report an uncaught synchronous exception, but cannot supply local React recovery. - A Promise rejection is expected: attach a rejection handler and handle the failure in the relevant async flow. Do not leave it unhandled just to rely on a global event.
- A Promise rejection reaches React through
use(promise)or the documented transition path: use a boundary to provide the UI fallback. - A failure reaches the browser globally: use
errorfor uncaught synchronous script errors andunhandledrejectionfor unhandled Promise rejections. Treat these as diagnostics, not as a substitute for recovery.
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