React Router Code Review

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name: react-router-code-review description: Reviews React Router code for proper data loading, mutations, error handling, and navigation patterns. Use when reviewing React Router v6.4+ code, loaders, actions, or navigation logic.

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React Router Code Review

Quick Reference

| Issue Type | Reference | |------------|-----------| | useEffect for data, missing loaders, params | references/data-loading.md | | Form vs useFetcher, action patterns | references/mutations.md | | Missing error boundaries, errorElement | references/error-handling.md | | navigate() vs Link, pending states | references/navigation.md |

Review Checklist

[ ] Data loaded via loader not useEffect

[ ] Route params accessed type-safely with validation

[ ] Using defer() for parallel data fetching when appropriate

[ ] Mutations use

or useFetcher not manual fetch

[ ] Actions handle both success and error cases

[ ] Error boundaries with errorElement on routes

[ ] Using isRouteErrorResponse() to check error types

[ ] Navigation uses over navigate() where possible

[ ] Pending states shown via useNavigation() or fetcher.state

[ ] No navigation in render (only in effects or handlers)

Valid Patterns (Do NOT Flag)

These patterns are correct React Router usage - do not report as issues:

useEffect for client-only data - Loaders run server-side; localStorage, window dimensions, and browser APIs must use useEffect

navigate() in event handlers - Link is for declarative navigation; navigate() is correct for imperative navigation in callbacks/handlers

Type annotation on loader data - useLoaderData() is a type annotation, not a type assertion

Empty errorElement at route level - Route may intentionally rely on parent error boundary

Form without action prop - Posts to current URL by convention; explicit action is optional

loader returning null - Valid when data may not exist; null is a legitimate loader return value

Using fetcher.data without checking fetcher.state - May be intentional when stale data is acceptable during revalidation

Context-Sensitive Rules

Only flag these issues when the specific context applies:

| Issue | Flag ONLY IF | |-------|--------------| | Missing loader | Data is available server-side (not client-only) | | useEffect for data fetching | Data is NOT client-only (localStorage, browser APIs, window size) | | Missing errorElement | No parent route in the hierarchy has an error boundary | | navigate() instead of Link | Navigation is NOT triggered by an event handler or conditional logic |

Gates (before reporting any finding)

Run in order. Pass each gate with evidence (paths, line refs, or a one-line quote from code)—not intuition alone.

Gate 1 — Scope the route surface

Pass when: You have repo path(s) to the route module, routes config entry, or layout that owns the behavior under review (write them in your notes before flagging).

Gate 2 — Context-sensitive match

Pass when: For every issue that maps to Context-Sensitive Rules, the Flag ONLY IF condition is satisfied with a one-line rationale tied to the code; for other checklist items, you have a concrete code citation (path + line or short excerpt).

Gate 3 — Non-issue patterns

Pass when: The behavior is not covered by Valid Patterns (Do NOT Flag) for that category.

Gate 4 — Verification protocol

Load and follow review-verification-protocol. Pass when: Its pre-report checklist (and any issue-type subsection that applies) is complete for each finding you will output.

When to Load References

Reviewing data fetching code → data-loading.md

Reviewing forms or mutations → mutations.md

Reviewing error handling → error-handling.md

Reviewing navigation logic → navigation.md

Review Questions

1. Is data loaded in loaders instead of effects? 2. Are mutations using Form/action patterns? 3. Are there error boundaries at appropriate route levels? 4. Is navigation declarative with Link components? 5. Are pending states properly handled?