---
source: https://iinventedlight.com/library/notes/nextjs-error-handling.md
title: "Error handling with error.js boundaries"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source_license: "MIT (vercel/next.js); prose restates cited source lines in own words"
license_family: nextjs-mit
attribution: "Summary by iinventedlight (AI-assisted). Sources: Next.js docs, Error handling, MIT (vercel/next.js); Next.js docs, error.js, MIT (vercel/next.js). Copyright (c) 2025 Vercel, Inc. MIT (https://raw.githubusercontent.com/vercel/next.js/canary/license.md)."
author: "iinventedlight (synthesis of cited sources); text drafted with AI assistance"
date: 2026-11-09
status: published
approved_by: "Cole Withington, 2026-11-09 13:04 PT: \"Yes, publish all 33 Next.js drafts\""
checked_on: 2026-11-09
as_of: 2026-11-09
confidence: medium
untested: "No Next.js app was run for this note; only the fetched documentation pages were read."
category: coding-references
topic_area: "code-web: Next.js errors"
tags: [nextjs, error-boundary, error.js]
client: Librarian
sources:
  - id: S1
    title: "Error handling"
    publisher: Next.js docs
    url: https://nextjs.org/docs/app/getting-started/error-handling
    accessed: 2026-11-09
    license: "MIT (vercel/next.js)"
  - id: S2
    title: "error.js"
    publisher: Next.js docs
    url: https://nextjs.org/docs/app/api-reference/file-conventions/error
    accessed: 2026-11-09
    license: "MIT (vercel/next.js)"
---
# Error handling with error.js boundaries

**Answer:** Errors can be divided into expected errors and uncaught exceptions. An error file shows fallback UI for unexpected runtime errors in a segment.

## Expected vs uncaught

Expected errors should be modeled as return values. Uncaught exceptions are unexpected errors that indicate bugs.

## error.js

An error file lets you handle unexpected runtime errors and display fallback UI. Next.js uses error boundaries to handle uncaught exceptions.

## See also

- [nextjs-not-found](https://iinventedlight.com/library/notes/nextjs-not-found/)
- [nextjs-loading-ui](https://iinventedlight.com/library/notes/nextjs-loading-ui/)

## Claims

- id: C1
  claim: Errors split into expected and uncaught.
  source: S1
  evidence: "Errors can be divided into two categories: [expected errors](#handling-expected-errors) and [uncaught exceptions](#handling-uncaught-exceptions)."

- id: C2
  claim: Model expected errors as return values.
  source: S1
  evidence: "Instead, model expected errors as return values."

- id: C3
  claim: error files show fallback UI.
  source: S2
  evidence: "An **error** file allows you to handle unexpected runtime errors and display fallback UI."

- id: C4
  claim: Next.js uses error boundaries for uncaught exceptions.
  source: S1
  evidence: "Next.js uses error boundaries to handle uncaught exceptions."

## Sources

- [S1] Error handling. Next.js docs. https://nextjs.org/docs/app/getting-started/error-handling . License: MIT (vercel/next.js). Accessed 2026-11-09.

- [S2] error.js. Next.js docs. https://nextjs.org/docs/app/api-reference/file-conventions/error . License: MIT (vercel/next.js). Accessed 2026-11-09.


License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted). Copyright (c) 2025 Vercel, Inc. Sources: Next.js docs (vercel/next.js on GitHub / nextjs.org), MIT (https://raw.githubusercontent.com/vercel/next.js/canary/license.md). Text was condensed and changed from the originals.

---

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