Apa saéh operator RxJS utama lan operator panyamarataan?

Question

Accepted Answer

**Operator RxJS** ngrubah, nyaring, lan ngabung aliran Observable. Sing paling penting — lan sing paling mbingungake — yaiku papat **operator panyamarataan** sing nangani Observable-of-Observable (contone: panggilan HTTP sing dipicu déning saben emisi saka aliran liyane).

## Operator transformasi/panyaring umum

```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
);
```

## Papat operator panyamarataan (bagian sing rumit)

Sédhela saben nilai saka sumber kudu ngdandani **liyane** Observable (kaya panggilan HTTP), sampeyan kudu "samarata" Observable internal. Papat beda ing **carane tangani tumpang-tindih**:

```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
```

## Kapan nggunakake saben-saben

```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
```

## Mnemonic

```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
```

## Mengapa itu penting

Operator panyamarataan minangka salah sawijining sing paling penting — lan sing paling sering disalahgunakake — alat RxJS ing Angular.

Pilihan sing salah nyebabake bug nyata: nggunakake `mergeMap` kanggo pencarian nuduhake asil basi (tanpa pembatalan); nggunakake `switchMap` kanggo penyimpanan berurutan mbatalake wong-wong samengko tengah-tengah.

Ngerti yen `switchMap` mbatalake (ideal kanggo pencarian), `concatMap` nglacak, `mergeMap` paralelkan, lan `exhaustMap` blok duplikat yaiku penting kanggo panganan asinkron sing bener ing kode Angular sing raket RxJS.