TypeScript Best Practices for Large Scale Applications

TypeScript has become the de facto standard for building large-scale JavaScript applications. Here are essential practices that will help you write more maintainable and scalable TypeScript code.

Strict Configuration

Always enable strict mode in your tsconfig.json:

{
  "compilerOptions": {
    "strict": true,
    "noImplicitReturns": true,
    "noImplicitOverride": true,
    "noUncheckedIndexedAccess": true
  }
}

Type-First Development

Define your types first, then implement:

// Define interfaces first
interface User {
  id: string;
  name: string;
  email: string;
  role: 'admin' | 'user';
}

interface UserRepository {
  findById(id: string): Promise<User | null>;
  create(user: Omit<User, 'id'>): Promise<User>;
  update(id: string, user: Partial<User>): Promise<User>;
}

// Then implement
class DatabaseUserRepository implements UserRepository {
  async findById(id: string): Promise<User | null> {
    // Implementation
  }
  
  // ... other methods
}

Utility Types

Leverage TypeScript's built-in utility types:

type CreateUserRequest = Omit<User, 'id'>;
type UpdateUserRequest = Partial<Pick<User, 'name' | 'email'>>;
type UserKeys = keyof User;

Discriminated Unions

Use discriminated unions for type safety:

type Result<T> = 
  | { success: true; data: T }
  | { success: false; error: string };

function handleResult<T>(result: Result<T>) {
  if (result.success) {
    // TypeScript knows result.data exists here
    console.log(result.data);
  } else {
    // TypeScript knows result.error exists here
    console.error(result.error);
  }
}

Conclusion

Following these practices will help you build more robust and maintainable TypeScript applications.