X'inhuma l-operaturi RxJS ewlenin u l-operaturi ta' taflija?

Question

Accepted Answer

**L-operaturi RxJS** jittrasformaw, jifiltraw u jgħaqqdu l-flussi Observable. L-aktar importanti — u l-aktar konfużi — huma l-erba **operaturi ta' taflija** li jmejżu Observable-of-Observable (eż. sejħa HTTP attivata minn kull emissjoni ta' stream ieħor).

## Operaturi ta' trasformazzjoni/filtru komuni

```ts
import { map, filter, tap, debounceTime, distinctUntilChanged, catchError } from "rxjs/operators";

source$.pipe(
  map(x => x * 2),                 // transform each value
  filter(x => x > 10),             // keep values passing a test
  tap(x => console.log(x)),        // side effect, doesn't change the stream
  debounceTime(300),               // wait for a pause before emitting (search inputs)
  distinctUntilChanged(),          // ignore consecutive duplicates
);
```

## L-erba operaturi ta' taflija (il-parti alqugħa)

Meta kull valur minn sors jieħu jiggjelda **Observable** ieħor (bħal talba HTTP), int trid "taflij" l-Observable intern. L-erba jitifferenzjaw fil-**mod kif jmejżu l-overlapping**:

```text
switchMap   → cancels the previous inner Observable when a new value arrives
mergeMap    → runs all inner Observables concurrently (no cancellation)
concatMap   → queues them, runs one at a time in order
exhaustMap  → ignores new values while an inner Observable is still running
```

## Meta tuża kull wieħed

```ts
// switchMap — type-ahead search: cancel the stale request when the user types again
this.searchInput.valueChanges.pipe(
  debounceTime(300),
  switchMap(query => this.api.search(query)) // only the LATEST query's result matters
).subscribe(results => this.results = results);

// mergeMap — fire independent requests in parallel (order doesn't matter)
from(ids).pipe(mergeMap(id => this.api.get(id)));

// concatMap — operations that MUST run in order (e.g. sequential saves)
actions$.pipe(concatMap(action => this.api.save(action)));

// exhaustMap — ignore repeated clicks while a login is in flight
this.loginClick$.pipe(exhaustMap(() => this.auth.login())); // ignore spam clicks
```

## Mnemonik

```text
switchMap  = "switch to the new one" (cancel old) → search
mergeMap   = "merge all" (parallel)              → independent requests
concatMap  = "concatenate" (sequential)          → ordered operations
exhaustMap = "exhaust current first" (ignore new) → prevent double-submit
```

## Għaliex hija importanti

L-operaturi ta' taflija huma fost l-aktar importanti — u l-aktar ħażin użati — għodod RxJS f'Angular.

L-għażla sbieħa tkawża bugs reali: l-użu ta' `mergeMap` għat-tiftix juri riżultati qegħda (l-ebda kanċellazzjoni); l-użu ta' `switchMap` għall-ħifz sekwenzjali jikkanċellaħom mid-dliegħ.

Il-għarfien li `switchMap` jikkanċella (ideal għat-tiftix), `concatMap` jordna, `mergeMap` paralelizza, u `exhaustMap` jibblokka l-duplikati hija essenzjali għall-immaniġġ async korrett fi kwalunkwe kodiċi Angular ħamiem RxJS.