Overview

Code inevitably becomes bloated over time. Cowork can help you analyze code structure, identify issues, propose refactoring suggestions, and even rewrite the code directly for you.

Use Cases

Modernizing legacy code
Eliminating duplicate code
Optimizing performance bottlenecks
Improving code readability
Adding type annotations
Splitting large functions/components

Steps

Step 1: Specify the Code to Analyze

Please help me analyze the code in the ~/Projects/myapp/src/ directory and find areas that need refactoring

Or target a specific file:

Analyze ~/Projects/myapp/src/utils.js - this file is too large and needs refactoring

Step 2: Get the Analysis Report

Claude will generate a detailed code analysis report:

## Code Analysis Report: utils.js

### File Overview
- Lines of code: 1,247 lines
- Number of functions: 42
- Complexity assessment: ⚠️ High

### Issues Found

1. **Duplicate Code** (Severity: High)
   - formatDate() and formatTime() share 80% similar code
   - validateEmail() and validatePhone() have duplicated logic

2. **Overly Long Functions** (Severity: Medium)
   - processUserData() has 156 lines, recommend splitting

3. **Inconsistent Naming**
   - Mixed use of camelCase and snake_case

4. **Missing Type Annotations**
   - Recommend adding TypeScript or JSDoc

### Refactoring Priority
1. 🔴 Extract common date handling functions
2. 🟡 Split processUserData()
3. 🟢 Standardize naming conventions

Step 3: Execute the Refactoring

Choose which refactoring to execute:

Please help me execute the first refactoring:
- Extract common date handling functions
- Create a new dateUtils.js file
- Update references in the original file

Step 4: Review and Confirm

Claude will show the code changes after refactoring:

// New file: dateUtils.js
+ export function formatDateTime(date, options) {
+   const { format = 'YYYY-MM-DD', includeTime = false } = options;
+   // ...unified date handling logic
+ }

// Modified: utils.js
- function formatDate(date) {
-   // 156 lines of duplicate code
- }
+ import { formatDateTime } from './dateUtils';
+ export const formatDate = (date) => formatDateTime(date, { format: 'YYYY-MM-DD' });

After confirmation, Claude will apply these changes.

Warning: Please ensure your code is committed to Git before refactoring. Cowork will modify your code files, so it's recommended to perform refactoring on a new branch.

Common Refactoring Patterns

Extract Functions

This code has a very long if-else block. Help me extract it into independent functions

Eliminate Magic Numbers

Find all magic numbers in the code and replace them with meaningful constants

Add Types

Add TypeScript type declarations to this JavaScript file

React Component Optimization

Analyze this React component:
- Are there unnecessary re-renders
- Is state management reasonable
- Can it be split into smaller components

Performance Optimization

Analyze performance issues in this code, especially loops and database queries

Tip: Have Claude preserve existing test cases during refactoring, or generate tests for the new code.

Supported Languages

Language	Support Level
JavaScript/TypeScript	⭐⭐⭐ Full support
Python	⭐⭐⭐ Full support
Java	⭐⭐⭐ Full support
Go	⭐⭐ Good support
Rust	⭐⭐ Good support
C/C++	⭐⭐ Good support
Others	⭐ Basic support

FAQ

Q: Will it break my code?

A: Claude will first show all changes for your review and will only execute after confirmation. It's recommended to save the current state with Git first.

Q: Can it handle large projects?

A: Yes! For large projects, it's recommended to refactor module by module gradually, rather than processing all files at once.

Q: Can functional consistency be guaranteed after refactoring?

A: Claude strives to ensure refactoring is an equivalent transformation, but it's recommended to run test cases after refactoring to confirm.

Real-World Example

"Inherited a 3-year-old project with messy code. Used Cowork to gradually refactor over two days, and the code quality improved significantly. Maintenance has been much easier since." — Frontend Developer