# TypeScript Best Practices for Large-Scale Applications

Building large-scale applications requires careful planning and adherence to best practices. TypeScript provides powerful tools to help maintain code quality as your application grows.

## Type Safety First

Always prefer explicit types over `any`:

```typescript
// Bad
function processData(data: any) {
return data.map((item: any) => item.value);
}

// Good
interface DataItem {
value: string;
id: number;
}

function processData(data: DataItem[]) {
return data.map(item => item.value);
}
```

## Utility Types

Leverage TypeScript's built-in utility types:

```typescript
interface User {
id: number;
name: string;
email: string;
password: string;
}

// Omit sensitive fields
type PublicUser = Omit;

// Make all fields optional
type PartialUser = Partial;

// Make all fields readonly
type ImmutableUser = Readonly;
```

## Generic Constraints

Use generic constraints to create flexible, type-safe functions:

```typescript
function getProperty(obj: T, key: K): T[K] {
return obj[key];
}

const user = { name: 'John', age: 30 };
const name = getProperty(user, 'name'); // Type: string
```

## Discriminated Unions

Use discriminated unions for type-safe state management:

```typescript
type LoadingState =
| { status: 'idle' }
| { status: 'loading' }
| { status: 'success'; data: string }
| { status: 'error'; error: Error };

function handleState(state: LoadingState) {
switch (state.status) {
case 'idle':
return 'Not started';
case 'loading':
return 'Loading...';
case 'success':
return state.data; // TypeScript knows data exists
case 'error':
return state.error.message; // TypeScript knows error exists
}
}
```

## Strict Configuration

Enable strict mode in your `tsconfig.json`:

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

## Conclusion

Following these best practices will help you build more maintainable and reliable TypeScript applications. Remember, the goal is to leverage TypeScript's type system to catch errors early and improve code quality.