Refactoring Code with Claude Code

Refactoring — restructuring existing code without changing its behavior — is one of the most tedious parts of development. Claude Code makes it fast and safe by understanding your entire codebase and making consistent changes across multiple files.

Simple Rename Refactoring

Rename a function or variable across your entire project:

> Rename the function getUserData to fetchUserProfile everywhere it's used in the project

Claude Code will find all usages — definitions, calls, imports, and tests — and rename them consistently.

Extract Function

Pull complex logic into its own function:

> In src/handlers/order.py, the process_order function is too long. Extract the payment validation logic into its own function.

Convert Patterns

Modernize your code by converting between patterns:

# Convert callbacks to async/await
> Convert all callback-based functions in src/services/ to use async/await

# Convert class components to functional
> Convert UserProfile.jsx from a class component to a functional component with hooks

# Convert to TypeScript
> Convert src/utils/helpers.js to TypeScript with proper type annotations

Restructure Project Layout

Reorganize your project’s directory structure:

> Move all API route handlers from routes/ into a new structure: 
controllers/ for business logic and routes/ for just route definitions.
Update all imports accordingly.

Simplify Complex Code

Ask Claude to simplify overly complex code:

> This function in src/utils/parser.py has deeply nested if-else statements. Refactor it to be more readable using early returns and guard clauses.

Add Type Safety

Incrementally add types to a JavaScript project:

> Add JSDoc type annotations to all exported functions in src/services/auth.js

Safe Refactoring Workflow

1. Ensure tests pass first — Ask Claude to run tests before refactoring
2. Refactor in small steps — Break large refactors into smaller chunks
3. Run tests after each change — Verify behavior is preserved
4. Review the diff — Use git diff to review all changes
5. Commit frequently — Create checkpoint commits during large refactors

Example workflow:

> Run the tests first to make sure everything passes

# Tests pass

> Now refactor the UserService to use dependency injection

# Claude makes the changes

> Run the tests again to verify nothing broke

# Tests still pass

> Commit these changes with a descriptive message

Summary

Claude Code handles refactoring across your entire codebase — from simple renames to major architectural changes. It tracks all references and ensures consistency. Next, we’ll learn how Claude Code works with Git.

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