Ni nini opereta muhimu za RxJS na opereta za kusambaza?

Question

IT Interview Practice · Accepted Answer

**Opereta za RxJS** hubadilisha, kusanga, na kuchanganya mikondo ya Observable. Muhimu zaidi — na yanayosasabishwa zaidi — ni **opereta nne za kusambaza** ambazo zinahusiana na Observable-za-Observable (mfano, kutoka kwa HTTP iliyoanzishwa na kila utendaji wa mlikizo mwingine).

## Opereta ya kawaida ya ubadilishaji/kusanga

```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
);
```

## Opereta nne za kusambaza (sehemu ngumu)

Kakati kila thamani kutoka vyanzo inahitaji kuanzisha **Observable** nyingine (kama ombi la HTTP), lazima "kusambaza" Observable ya ndani. Nne hutofautiana kwa **jinsi wanavyoshughulikia kuingiliana**:

```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
```

## Ni lini kutumia kila moja

```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
```

## Njia ya kukumbuka

```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
```

## Kwa nini ikihami

Opereta za kusambaza ni miongoni mwa muhimu zaidi — na yanayotumiwa vibaya zaidi — zana za RxJS katika Angular.

Kuchagua vibaya husababisha hitilafu halisi: kutumia `mergeMap` kwa utaftaji kuonyesha matokeo yaliyozaa (hakuna kukataza); kutumia `switchMap` kwa akifuatia kukataza zao wakati wa ndege.

Kujua kuwa `switchMap` kinachozaa (bora kwa utaftaji), `concatMap` kila kitu, `mergeMap` sambamba, na `exhaustMap` kuzuia nakala ni muhimu kwa tahadhari sahihi ya async katika kode yoyote ya RxJS-nyingi ya Angular.

Opereta ya kawaida ya ubadilishaji/kusanga

Opereta nne za kusambaza (sehemu ngumu)

Ni lini kutumia kila moja

Njia ya kukumbuka

Kwa nini ikihami

Maswali yanayohusiana