Cursor refactor legacy component workflow: make small safe changes

Use Cursor to refactor a messy legacy component with boundaries, tests, diffs, and review checkpoints instead of one risky rewrite.

AI coding tools are useful for refactoring, but they are also very good at making confident changes you did not ask for. A legacy component usually has hidden behavior: odd props, old CSS classes, event handlers, data fallbacks, and small bugs that users have learned to rely on. A full rewrite is the dangerous path.

This workflow uses Cursor as a refactoring assistant while keeping you in control of scope. The goal is not to make the component beautiful in one session. The goal is to reduce risk in small, reviewable steps.

What you will build

You will create a safe refactor loop:

• Ask Cursor to map the current behavior
• Add or identify tests
• Extract one helper
• Review the diff
• Repeat only if the previous step stayed safe

Use this for React components, Vue components, old utility files, or server handlers.

Step 1 - ask for a behavior map

Do not start with "refactor this." Start with analysis.

Analyze this component without editing it.
List:
1. What props or inputs it accepts
2. What user-visible behavior it controls
3. What side effects it has
4. What logic could be extracted safely
5. What changes would be risky
Do not propose a rewrite yet.

Read the answer critically. If Cursor misses important behavior, tell it what it missed before continuing.

Step 2 - define the safety boundary

Write a short constraint block.

Refactor constraints:
- Preserve existing UI and behavior
- Do not rename public props
- Do not change CSS class names
- Do not add dependencies
- Prefer extracting pure helper functions
- Make one change at a time

Paste this into every refactor request. AI tools do not always remember constraints across a long chat.

Step 3 - add characterization tests

If tests already exist, run them before changing code. If there are no tests, add one or two small tests around current behavior.

Examples:

• Rendering with the default props
• Rendering an empty state
• Clicking the main button
• Formatting a date or status label

The test does not need to cover everything. It needs to protect the behavior you are about to touch.

Step 4 - ask for one extraction

Pick one safe target. For example, a status label map.

Using the constraints below, extract only the status label logic into a pure helper.
Do not change JSX structure.
Do not rename props.
Do not change CSS classes.
Show the diff and explain why behavior is preserved.
 
[Paste constraints]

Review the actual diff. Ignore the explanation if the diff says otherwise. The code is the evidence.

Step 5 - run tests and inspect the UI

After every change, run the smallest useful verification:

npm test -- status-label
npm run lint

If the project has no unit tests, run the app and manually check the states you touched. Do not queue up five refactors before checking the first one.

Step 6 - repeat with a commit-sized change

A good AI-assisted refactor commit should be easy to describe:

Extract status label helper without changing component behavior.

Bad commit:

Refactor component and clean things up.

If the description needs the word "and" three times, the change is too large.

Common mistakes

Avoid these:

• Asking Cursor to rewrite the component from scratch
• Accepting unrelated formatting churn
• Changing names that other files import
• Mixing refactor with new features
• Trusting the chat explanation more than the diff

Final checklist

Before merging:

• Tests pass
• The visual behavior you touched still works
• Public props did not change
• CSS class names did not change unless planned
• The diff contains only the intended refactor
• The commit message explains a behavior-preserving change

FAQ

Should Cursor rewrite the whole component at once?

No. Ask for analysis first, then make one behavior-preserving change at a time.

What is the safest first refactor?

Extract pure formatting or mapping logic into a helper with tests.

How do I stop AI from changing behavior?

Give explicit constraints, inspect the diff, and run tests after every small change.

Should I accept all suggested edits?

No. Treat AI edits like a pull request from another engineer.

What if there are no tests?

Add characterization tests or snapshot the current behavior before refactoring.