TypeScript Best Practices for Large-Scale Applications

TypeScript is essential for large-scale applications. Here are the best practices that will make your code more maintainable, robust, and developer-friendly.

Strict Type Configuration

Enable strict mode in your tsconfig.json:

{
  "compilerOptions": {
    "strict": true,
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "noImplicitReturns": true,
    "noFallthroughCasesInSwitch": true
  }
}

Type Definitions

Create comprehensive type definitions:

// User types
interface User {
  id: string;
  email: string;
  profile: UserProfile;
  preferences: UserPreferences;
}

interface UserProfile {
  firstName: string;
  lastName: string;
  avatar?: string;
}

// API response types
interface ApiResponse {
  data: T;
  status: 'success' | 'error';
  message?: string;
}

Generic Types

Use generics for reusable components:

interface Repository {
  findById(id: string): Promise;
  save(entity: T): Promise;
  delete(id: string): Promise;
}

class UserRepository implements Repository {
  async findById(id: string): Promise {
    // Implementation
  }
}

Utility Types

Leverage TypeScript's built-in utility types:

• Partial<T>: Makes all properties optional
• Pick<T, K>: Select specific properties
• Omit<T, K>: Exclude specific properties
• Record<K, V>: Create object types

Error Handling

Implement proper error handling with types:

class AppError extends Error {
  constructor(
    message: string,
    public statusCode: number,
    public isOperational: boolean = true
  ) {
    super(message);
    this.name = this.constructor.name;
  }
}

type Result = 
  | { success: true; data: T }
  | { success: false; error: E };

Testing with Types

Use types for better testing:

• Mock types for test data
• Type-safe test utilities
• Assertion helpers with proper types

Conclusion

TypeScript best practices evolve with your application. Start with strict configuration, use comprehensive types, and gradually adopt advanced patterns as your codebase grows.