TypeScript Best Practices for Large-Scale Applications

TypeScript has become the go-to choice for large-scale JavaScript applications. This guide covers essential practices for building maintainable and scalable TypeScript applications.

Project Structure and Configuration

Strict Configuration

Enable strict mode for better type safety:

```json

{

"compilerOptions": {

"strict": true,

"noImplicitAny": true,

"noImplicitReturns": true,

"noFallthroughCasesInSwitch": true

}

}

```

Path Mapping

Use path mapping for cleaner imports:

```json

{

"compilerOptions": {

"baseUrl": ".",

"paths": {

"@/": ["src/"],

"@/components/": ["src/components/"],

"@/utils/": ["src/utils/"]

}

}

}

```

Type Definitions and Interfaces

Prefer Interfaces for Object Types

Interfaces provide better error messages and are more extensible:

```typescript

interface User {

id: string;

name: string;

email: string;

}

```

Use Utility Types

Leverage TypeScript's built-in utility types:

```typescript

type PartialUser = Partial;

type UserEmail = Pick;

type UserWithoutId = Omit;

```

Advanced Patterns

Generic Constraints

Use generic constraints for type safety:

```typescript

function getProperty(obj: T, key: K): T[K] {

return obj[key];

}

```

Discriminated Unions

Use discriminated unions for type-safe state management:

```typescript

type LoadingState =

| { status: 'loading' }

| { status: 'success'; data: any }

| { status: 'error'; error: string };

```

Error Handling

Result Types

Implement Result types for explicit error handling:

```typescript

type Result =

| { success: true; data: T }

| { success: false; error: E };

```

Testing with TypeScript

Type-Safe Testing

Ensure your tests are type-safe:

```typescript

interface TestUser {

id: string;

name: string;

}

const mockUser: TestUser = {

id: '1',

name: 'John Doe'

};

```

Performance Considerations

Type-Only Imports

Use type-only imports to reduce bundle size:

```typescript

import type { User } from './types';

```

Lazy Loading Types

Use dynamic imports for types that are only needed conditionally.

Conclusion

Following these TypeScript best practices will help you build more maintainable, scalable, and type-safe applications. The key is to leverage TypeScript's powerful type system while keeping your code readable and maintainable.