TypeScript Best Practices - Essential Patterns

Introduction

TypeScript has become the de facto standard for building large-scale JavaScript applications. However, to truly leverage its power, you need to follow best practices that ensure type safety, maintainability, and developer productivity. This guide covers essential patterns that will elevate your TypeScript code.

1. Enable Strict Mode

Always enable strict mode in your tsconfig.json. This enables all strict type-checking options and catches potential bugs early.

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

2. Avoid Using 'any'

The any type defeats the purpose of TypeScript. Use unknown when the type is truly unknown, or define proper types.

❌ Bad:

function process(data: any) {
  return data.value;
}

✅ Good:

function process(data: unknown) {
  if (isValidData(data)) {
    return data.value;
  }
}

3. Use Type Inference

Let TypeScript infer types when possible. Explicit types should be used for function parameters and complex return types, but let the compiler infer simple cases.

⚠️ Over-specified:

const count: number = 5;
const name: string = "John";

✅ Better:

const count = 5;
const name = "John";

4. Leverage Union Types

Union types allow a value to be one of several types. They're powerful for modeling different states and preventing invalid combinations.

type Status = 'idle' | 'loading' | 'success' | 'error';

interface ApiState {
  status: Status;
  data?: any;
  error?: Error;
}

5. Create Reusable Generic Types

Generics make your code flexible and reusable while maintaining type safety.

type ApiResponse<T> = {
  data: T;
  status: number;
  message: string;
};

async function fetchUser(): Promise<ApiResponse<User>> {
  // Implementation
}

6. Use Utility Types

TypeScript provides built-in utility types that help transform types. Learn and use them effectively.

Partial<T> - Makes all properties optional
Required<T> - Makes all properties required
Pick<T, K> - Creates a type by picking specific properties
Omit<T, K> - Creates a type by omitting specific properties
Record<K, T> - Creates an object type with specific keys

7. Type Guards for Runtime Checks

Use type guards to narrow types at runtime and provide type safety for dynamic data.

function isUser(obj: any): obj is User {
  return 'id' in obj && 'name' in obj && 'email' in obj;
}

if (isUser(data)) {
  // TypeScript knows data is User here
  console.log(data.email);
}

8. Prefer Interfaces for Object Shapes

Use interfaces for defining object shapes as they can be extended and merged. Use type aliases for unions, intersections, and complex types.

interface User {
  id: string;
  name: string;
}

interface AdminUser extends User {
  permissions: string[];
}

Conclusion

Following these TypeScript best practices will help you write more maintainable, type-safe code. Remember that TypeScript is a tool to help you catch bugs early and improve developer experience. Embrace its features, and your codebase will thank you.