rxjs-implementation

# RxJS Implementation Skill

## Quick Start

### Observable Basics
```typescript
import { Observable } from 'rxjs';

// Create observable
const observable = new Observable((observer) => {
  observer.next(1);
  observer.next(2);
  observer.next(3);
  observer.complete();
});

// Subscribe
const subscription = observable.subscribe({
  next: (value) => console.log(value),
  error: (error) => console.error(error),
  complete: () => console.log('Done')
});

// Unsubscribe
subscription.unsubscribe();
```

### Common Operators
```typescript
import { map, filter, switchMap, takeUntil } from 'rxjs/operators';

// Transformation
data$.pipe(
  map(user => user.name),
  filter(name => name.length > 0)
).subscribe(name => console.log(name));

// Higher-order
userId$.pipe(
  switchMap(id => this.userService.getUser(id))
).subscribe(user => console.log(user));
```

## Subjects

### Subject Types
```typescript
import { Subject, BehaviorSubject, ReplaySubject } from 'rxjs';

// Subject - No initial value
const subject = new Subject<string>();
subject.next('hello');

// BehaviorSubject - Has initial value
const behavior = new BehaviorSubject<string>('initial');
behavior.next('new value');

// ReplaySubject - Replays N values
const replay = new ReplaySubject<string>(3);
replay.next('one');
replay.next('two');
```

### Service with Subject
```typescript
@Injectable()
export class NotificationService {
  private messageSubject = new Subject<string>();
  public message$ = this.messageSubject.asObservable();

  notify(message: string) {
    this.messageSubject.next(message);
  }
}

// Usage
constructor(private notification: NotificationService) {
  this.notification.message$.subscribe(msg => {
    console.log('Notification:', msg);
  });
}
```

## Transformation Operators

```typescript
// map - Transform values
source$.pipe(
  map(user => user.name)
)

// switchMap - Switch to new observable (cancel previous)
userId$.pipe(
  switchMap(id => this.userService.getUser(id))
)

// mergeMap -