TypeScript Professional

Strict TypeScript patterns for professional development.

Instructions

1. Strict Mode Configuration

Always enable strict mode in tsconfig.json:

{
  "compilerOptions": {
    "strict": true,
    "noImplicitAny": true,
    "strictNullChecks": true,
    "noUnusedLocals": true,
    "noUnusedParameters": true
  }
}

2. Naming Conventions

Type	Convention	Example
Interface	PascalCase, prefix with I (optional)	User, IUserService
Type	PascalCase	UserRole, ApiResponse
Enum	PascalCase	Status, Direction
Function	camelCase	getUserById, calculateTotal
Variable	camelCase	userName, isLoading
Constant	UPPER_SNAKE_CASE	MAX_RETRY_COUNT, API_URL

3. Type vs Interface

// ✅ Interface for object shapes
interface User {
  id: string;
  name: string;
  email: string;
}

// ✅ Type for unions, intersections, primitives
type Status = 'pending' | 'active' | 'inactive';
type ApiResponse<T> = { data: T; error: null } | { data: null; error: string };

4. Never Use any

// ❌ Bad
function process(data: any) { ... }

// ✅ Good - use unknown and narrow
function process(data: unknown) {
  if (typeof data === 'string') {
    return data.toUpperCase();
  }
}

// ✅ Good - use generics
function process<T>(data: T): T { ... }

5. Utility Types

// Partial - all optional
type PartialUser = Partial<User>;

// Required - all required
type RequiredUser = Required<User>;

// Pick - select specific
type UserName = Pick<User, 'name'>;

// Omit - exclude specific
type UserWithoutId = Omit<User, 'id'>;

// Record - key-value mapping
type UserMap = Record<string, User>;

6. Function Types

// ✅ Explicit return types for public APIs
function getUser(id: string): Promise<User | null> {
  // ...
}

// ✅ Arrow function with types
const add = (a: number, b: number): number => a + b;

7. Generics

// ✅ Constrained generics
function getProperty<T, K extends keyof T>(obj: T, key: K): T[K] {
  return obj[key];
}

// ✅ Default generic types
interface ApiResponse<T = unknown> {
  data: T;
  status: number;
}

References

• TypeScript Handbook
• TypeScript Deep Dive