best-practices

Use this skill when implementing features or refactoring code to follow established patterns.

Checklist

Validation Before Claiming Success

• [ ] Unit tests passing ≠ code is correct
  • Check application logs for warnings and timing issues
  • Test with real workloads when possible
  • Verify behavior matches requirements, not just tests
• [ ] Performance matters
  • Check for unnecessary re-renders (React DevTools)
  • Verify bundle size impact for new dependencies
  • Test with realistic data volumes

Question Patterns Before Copying

When copying code from elsewhere in the codebase:

• [ ] What problem does this solve?
  • Understand the original use case
  • Verify it applies to your situation
• [ ] Does this pattern apply here?
  • Consider the context differences
  • Don't blindly copy without understanding
• [ ] What's the performance impact?
  • Understand computational cost
  • Consider alternative approaches

Refactoring Guidelines

• [ ] Update tests when behavior/API contracts change
  • Don't keep tests passing by mocking new behavior
  • Update assertions to match new contracts
• [ ] Prefer editing existing files over creating new ones
  • Don't create new files for minor changes
  • Keep related code together
• [ ] Component Encapsulation
  • Use hooks internally instead of passing derived values as props
  • Avoid unnecessary prop drilling

Examples:

// ✅ Good - component encapsulates its own dependencies
export const ImageGrid: FC<{ images: Image[] }> = ({ images }) => {
  const baseURL = useBackendUrl()
  return <div>{/* render images with baseURL */}</div>
}

// ❌ Avoid - unnecessary prop drilling
export const ImageGrid: FC<{ images: Image[]; baseURL: string }> = ({
  images,
  baseURL
}) => {
  return <div>{/* render images */}</div>
}

Extract Duplicated Configuration

• [ ] Identical configs in multiple files → Extract to constants
  • Look for repeated option objects
  • Look for repeated configuration values
  • Create shared constants file
  • Import from single source of truth

Example:

// ❌ Bad - duplicated configuration
// file1.ts
const options = { timeout: 5000, retries: 3 }

// file2.ts
const options = { timeout: 5000, retries: 3 }

// ✅ Good - extracted to shared constant
// constants.ts
export const API_OPTIONS = { timeout: 5000, retries: 3 }

// file1.ts & file2.ts
import { API_OPTIONS } from './constants'

Verify API Behavior Before Refactoring

• [ ] Read official documentation for the API
  • Don't assume behavior based on naming
  • Check for version-specific differences
  • Understand return types and possible values
• [ ] Don't add defensive code based on assumptions
  • Only add guards/checks if behavior actually differs
  • Test edge cases to verify actual behavior
• [ ] Test cases should match real API behavior
  • Don't test for imagined edge cases
  • Mock realistic responses, not theoretical ones

Example:

// ❌ Bad - defensive code based on assumptions
const value = api.getValue()
if (value === null || value === undefined || value === '') {
  // Assuming getValue() can return null/undefined/empty
}

// ✅ Good - verified that getValue() only returns string or throws
try {
  const value = api.getValue() // Documentation: returns string or throws
  // Use value directly
} catch (error) {
  // Handle error case
}

Research First

• [ ] Check official documentation before implementing
  • Libraries: Read the official docs, not blog posts
  • APIs: Check the specification/documentation
  • Frameworks: Follow official guides and examples
• [ ] Check existing patterns in the codebase
  • Search for similar implementations
  • Follow established conventions
  • Ask if unsure about approach

Common Pitfalls

Over-validation:

• Don't add checks for impossible states
• Trust internal APIs and framework guarantees
• Only validate at system boundaries (user input, external APIs)

Premature abstraction:

• Don't create helpers for one-time operations
• Don't design for hypothetical future requirements
• Three similar lines is better than premature abstraction

Ignoring performance:

• Tests passing ≠ code is performant
• Check re-render count, bundle size, load times
• Profile before and after changes

Reference

See @docs/CODING_STYLE.md for detailed coding standards.