Menene muhimman RxJS operators da flattening operators?

Question

Accepted Answer

**RxJS operators** suna canzawa, tacewa, da haɗe Observable streams. Mafi mahimmi — da mafi ruɗanin — su ne hudu **flattening operators** waɗanda suke duba Observables-of-Observables (misali karbar HTTP da aka bugi ta kowane abubuwan da aka aika daga jiya watsi).

## Common transformation/filter operators

```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
);
```

## The four flattening operators (the tricky part)

Lokacin da kowane ƙima daga tushen zai bugi **wani" Observable (kamar bugi HTTP), dole ne ku "taɓata" Observable na ciki. Hudu sun banbanta cikin **yadda suke jinka overlap**:

```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
```

## When to use each

```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
```

## A 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
```

## Me ya sa haka mahimmaci

Flattening operators suna tsakanin mafi mahimman — da mafi yawan amfani da shi ba daidai — RxJS kayan aiki a cikin Angular.

Zaɓi ɗalibin sa yana haifar da ainihin kudu: amfani da `mergeMap` don bincike yana nuna tsofaffin sakamakon (babu soke); amfani da `switchMap` don ajiyar jeri yana soke su tsakanin jirgin.

Sanin cewa `switchMap` yana soke (mafi kyau don bincike), `concatMap` yana odar, `mergeMap` yana yin parallel, da `exhaustMap` yana toshe dumarewa shine dole don daidaitaccen async jiyya a cikin duk RxJS-heavy Angular code.