# Prompt to Refactor a React Component Safely

> Structured AI agent prompt to refactor a complex React component with a read-audit-refactor-verify loop that prevents regressions.

**Type:** Prompt  
**Tools:** Cursor, Claude Code, Codex, Windsurf  
**Stack:** Next.js, TypeScript  
**Difficulty:** medium  
**Updated:** 2026-06-08

---

Use this prompt to drive a disciplined component refactor — making the agent audit
before changing, extract sub-components one at a time, and verify types after each
step, rather than rewriting the whole file in one shot.

## Main Prompt

```txt title="Main Prompt"
You are refactoring a React component in a Next.js App Router TypeScript project.
The target file is: [INSERT PATH, e.g. src/components/ProductCard.tsx]

Refactor goal: split a large monolithic component into smaller, reusable pieces without
changing any observable behavior or UI output.

Follow these phases exactly — do not skip or combine them.

Phase 1 — Audit (no changes):
  - List every `useState` and `useEffect` call and what it manages.
  - List every prop the component accepts (with types).
  - List any inline sub-sections that could be extracted (e.g., a header, a list, a footer).
  - Identify any duplicated logic (e.g., the same conditional repeated).
  Output the audit as a numbered list. Stop and wait for my review.

Phase 2 — Extract pure sub-components (one at a time):
  - For each extractable section identified: create a new file, move the JSX and its
    required props, export a typed interface for the props, import and use it in the parent.
  - After each extraction: run `bun run typecheck`. If it fails, fix the error before
    the next extraction.

Phase 3 — Extract custom hooks:
  - If any `useEffect` + `useState` pair manages a single concern (e.g., a data fetch,
    a keyboard listener), extract it to `src/hooks/use<Name>.ts`.
  - After each extraction: run `bun run typecheck`.

Phase 4 — Remove duplication:
  - Consolidate any repeated conditional logic into a shared helper.
  - Do NOT change the logic — only the structure.

Phase 5 — Final verify:
  - Run `bun run typecheck`.
  - Show a summary of all files created or edited.
  - Do NOT change any business logic, API calls, or UI output.

After each phase, show the diff and wait for my confirmation before proceeding.
```

## Implementation Notes

- The key constraint is behavior preservation: the refactor must be a pure structural change.
  Ask the agent to confirm this after each phase by checking the diff contains no logic changes.
- TypeScript is the safety net here: running `typecheck` after each extraction catches
  missing props or incorrect type narrowing immediately.
- Custom hook extraction is only safe when the hook's state is local to a single component instance.
  If state needs to be shared, do not extract — note it and stop.

## Expected File Changes

```txt
src/components/<name>.tsx            (edited — original component, slimmed down)
src/components/<name>Header.tsx      (new — extracted sub-component)
src/components/<name>List.tsx        (new — extracted sub-component)
src/hooks/use<name>.ts               (new — extracted hook, if applicable)
```

## Acceptance Criteria

- `bun run typecheck` exits 0 after each phase.
- The parent component props interface is unchanged.
- No `any` types are introduced.
- UI output is pixel-identical before and after (verified by visual inspection or snapshot tests).

## Test Commands

```bash
bun run typecheck
bun run build
# if snapshot tests exist:
bun test --update-snapshots   # run BEFORE refactor to capture baseline
# then after refactor:
bun test                       # snapshots should pass without update
```

## Common AI Mistakes

- Changing a callback's behavior while extracting it to a sub-component (e.g., adding `useCallback`
  with wrong deps, silently changing when it fires).
- Extracting a hook that holds state shared across multiple component instances, causing state loss.
- Introducing `any` types on extracted component props to avoid resolving complex generics.
- Skipping `typecheck` between phases and accumulating errors that are hard to trace.

## Fix Prompt

```txt title="Fix Prompt"
A type error appeared after an extraction or behavior changed. Fix in order:
1. Run `bun run typecheck` and show me only the errors — do not fix anything yet.
2. For each error: if it is a missing prop, add it to the extracted component's props interface.
   If it is an `any` type, resolve it using the type from the parent component's existing interface.
3. If any logic changed (a conditional, an effect dependency, a callback), revert that specific
   change only. Show the revert diff before applying it.
```