# `react-doctor/prefer-function-component`

Re-write the class component as a function component using hooks.

- **Status:** Active
- **Category:** Architecture
- **Assessment:** Evidence-required risk
- **Required evidence:** source code, repository context
- **Default configuration:** Disabled until configured
- **Default severity:** warn
- **Scope:** All supported frameworks
- **Active when:** off by default (opt-in)
- **Requirements:** react
- **Priority:** 22 (P3)
- **Source:** oxlint-plugin-react-doctor
- **Rule set:** oxlint-plugin-react-doctor 0.9.3 (prompt schema 2)
- **Documentation:** [Official documentation](https://oxc.rs/docs/guide/usage/linter/rules/react/prefer-function-component)

## Validation prompt

Confirm the detector match and collect the required evidence before deciding whether an edit is warranted.

Fires on any ClassDeclaration or ClassExpression that extends Component, PureComponent, React.Component, or React.PureComponent: i.e. an ES6 React class component that could be a function with hooks. By default, error-boundary classes (those defining componentDidCatch or getDerivedStateFromError) are exempt, but setting allowErrorBoundary:false makes them fire too.

Suppress when: when allowJsxUtilityClass:true is configured the rule also flags non-Component classes that merely contain JSX, which may be legitimate render-helper utilities rather than components needing conversion.

## Evidence boundary

The diagnostic proves only that the detector's modeled source pattern matched. It does not prove runtime impact, product intent, rendered failure, or that one remediation is correct.

Establish the environment, explicit repository policy, relevant exceptions, and required rendered or runtime evidence before deciding the occurrence. This page’s Assessment and Required evidence fields define the review contract.

Default severity is registry metadata. Use the occurrence's JSON severity after repository configuration when ordering real findings.

Record one outcome:

- **Confirmed failure:** The required evidence establishes the violation.
- **Rejected:** A documented exception or false-positive predicate applies.
- **Needs evidence:** Named evidence can still be collected.
- **Unavailable:** Required evidence cannot be collected in this run.
- **Waived with evidence:** An authorized, scoped exception applies to an established failure.
- **Observation:** The review records an optional tradeoff without claiming a defect.

A waiver records its scope, authority, evidence, and review or expiry condition. It is not a pass or false positive.

## Fix prompt

Apply this candidate correction only after the required evidence confirms the risk.

Convert only after mapping behavior rather than translating lifecycle names mechanically. Derive render data directly, move event-owned work to handlers, and use Effects only for external synchronization with dependencies and cleanup that preserve mount/update/unmount timing. Preserve getSnapshotBeforeUpdate semantics explicitly, and keep a class error boundary because hooks have no equivalent. Add focused tests for lifecycle ordering, refs, subscriptions, and error handling before and after the migration. See https://oxc.rs/docs/guide/usage/linter/rules/react/prefer-function-component

## Repository-wide copy prompt

Use this only for a repository-wide pass after validating each occurrence. For one occurrence, use the occurrence-level guidance above.

````text
Fix every confirmed `react-doctor/prefer-function-component` diagnostic in the current repository.

Required change:
- Convert only after mapping behavior rather than translating lifecycle names mechanically. Derive render data directly, move event-owned work to handlers, and use Effects only for external synchronization with dependencies and cleanup that preserve mount/update/unmount timing. Preserve getSnapshotBeforeUpdate semantics explicitly, and keep a class error boundary because hooks have no equivalent. Add focused tests for lifecycle ordering, refs, subscriptions, and error handling before and after the migration. See https://oxc.rs/docs/guide/usage/linter/rules/react/prefer-function-component.

Validation before editing:
Fires on any ClassDeclaration or ClassExpression that extends Component, PureComponent, React.Component, or React.PureComponent: i.e. an ES6 React class component that could be a function with hooks. By default, error-boundary classes (those defining componentDidCatch or getDerivedStateFromError) are exempt, but setting allowErrorBoundary:false makes them fire too.

Suppress when: when allowJsxUtilityClass:true is configured the rule also flags non-Component classes that merely contain JSX, which may be legitimate render-helper utilities rather than components needing conversion.

Constraints:
- Make the smallest change that fixes the root cause.
- Preserve behavior and interfaces unrelated to this diagnostic.
- Reuse existing project components, utilities, and conventions.
- Do not introduce render-phase side effects, render-phase state updates, or Hooks rule violations.
- Adapt identifiers and framework details instead of copying blindly.
- Do not disable the rule or suppress matching code.
- Confirm this rule is enabled for the project: `off by default (opt-in)`.

Assessment:
- Record detector evidence, applicability facts, assumptions, missing evidence, and the rule class for this occurrence.
- Return one outcome: Confirmed failure, Rejected, Needs evidence, Unavailable, Waived with evidence, or Observation.
- A waiver records the established failure, scope, authority, evidence, and review or expiry condition. It is not a pass or false positive.

Verification:
- Run focused tests for the changed behavior.
- Run React Doctor and confirm this diagnostic no longer appears from changed code.
- Run an unfiltered scan of the affected scope before claiming no cross-category regression.
- Report the files changed and any checks you could not run.
````