Cad iad oibreoirí RxJS práinnciúla agus na hoibreoirí flapála?

Question

Accepted Answer

**Oibreoirí RxJS** a chlaochlaíonn, a scagann, agus a chomhcheanglaíonn sruthanna Observable. Is iad na ceithre **oibreoirí flapála** — an rud is tábhachtaí agus is mearbhall — na cinn is thábhachtaí, agus baineanns siad le hObservables-of-Observables (mar shampla, glaoch HTTP atá spreagtha ag gach astarraingt de shruth eile).

## Oibreoirí claochlaitheocha/scagtha coitianta

```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
);
```

## Na ceithre oibreoirí flapála (an chuid dhraíochta)

Nuair is gá go spreagfaidh gach luach ó fhoinse **oibreoirí eile** Observable (cosúil le iarratas HTTP), ní mór duit an Observable inmheánach a "fhlapáil". Is éagsúil iad na ceithre ar **conas iad a dhéileáil le forshíoladh**:

```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
```

## Cathain a úsáid gach ceann

```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
```

## Mnemóinic

```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
```

## Cén fáth a bhfuil sé tábhachtach

Is iad na hoibreoirí flapála ar na huirlisí RxJS is thábhachtaí — agus is minic a dhéantar iad a mhíúsáid — in Angular.

Baineann rogha thuathalach gnéithe fíora: má úsáideann tú `mergeMap` do thóraighe, taispeántar torthaí sean-aimseartha (gan chur ar ceal); má úsáideann tú `switchMap` do shábhálacha seicheamhúla, chuireann siad ar ceal iad ar foluain.

Tá sé riachtanach a bheith i bhfios gur cuireann `switchMap` ar ceal (an-oiriúnach do thóraighe), go bhfuil `concatMap` socraithe, go bhfuil `mergeMap` ag soláthar go comhthreomhar, agus go bhfuil `exhaustMap` ag bac ar dhúbailte, ar bhealach éigeantach do dhéileáil cheart le asincronach in aon chód Angular a bhfuil go leor RxJS ann.