Deprecated APIs in RxJS v7

This page documents all APIs that are deprecated in RxJS v7. These APIs still work but will be removed in RxJS v8. Migrate to the recommended alternatives as soon as possible.

Promise Conversion

toPromise()

Deprecated in v7, will be removed in v8. Use firstValueFrom() or lastValueFrom() instead.

The toPromise() method has been deprecated because:

The name doesn’t indicate which value (first or last) will be used
The return type Promise<T | undefined> can be confusing
The behavior with empty observables is inconsistent

Migration to lastValueFrom

Use lastValueFrom() when you want the final emitted value:

import { interval } from 'rxjs';
import { take } from 'rxjs/operators';

async function example() {
  const source$ = interval(1000).pipe(take(5));
  const result = await source$.toPromise();
  console.log(result); // 4 (last value)
}

Migration to firstValueFrom

Use firstValueFrom() when you want the first emitted value:

import { interval } from 'rxjs';
import { map } from 'rxjs/operators';

async function example() {
  // With toPromise, you'd need take(1)
  const source$ = interval(1000).pipe(
    map(x => x * 2),
    take(1)
  );
  const result = await source$.toPromise();
  console.log(result); // 0
}

Handling Empty Observables

EmptyError vs. default values

import { EMPTY } from 'rxjs';

async function example() {
  const result = await EMPTY.toPromise();
  console.log(result); // undefined
}

Warning: Only use these functions with observables that will complete. For potentially infinite observables, add timeout, take, takeWhile, or takeUntil to prevent memory leaks.

Multiple Function Arguments

Deprecated in v6.4, will be removed in v8. Use observer objects instead of multiple function arguments.

Passing multiple function arguments to subscribe() is deprecated. This affects both subscribe() and the tap operator.

Why This Was Deprecated

Readability: subscribe(doSomething, doSomethingElse, lol) is unclear
Future flexibility: Second argument may be used for configuration (AbortSignal, etc.)
Null confusion: subscribe(null, null, onComplete) is hard to read

Migration Examples

import { of } from 'rxjs';

of(1, 2, 3).subscribe(
  value => console.log(value),
  err => console.error(err),
  () => console.log('complete')
);

import { throwError } from 'rxjs';

throwError(() => new Error('oops')).subscribe(
  null,
  err => console.error(err)
);

import { EMPTY } from 'rxjs';

EMPTY.subscribe(
  null,
  null,
  () => console.log('complete')
);

Single next callback is still fine: of(1, 2, 3).subscribe(v => console.log(v)) is the recommended pattern when you only need the next callback.

tap Operator

The same deprecation applies to tap:

import { of } from 'rxjs';
import { tap } from 'rxjs/operators';

of(1, 2, 3).pipe(
  tap(
    v => console.log('next:', v),
    err => console.error('error:', err),
    () => console.log('complete')
  )
).subscribe();

Multicasting APIs

Deprecated in v7, will be removed in v8. Multicasting APIs have been simplified to connectable, connect, and share.

ConnectableObservable

import { ConnectableObservable, timer, Subject } from 'rxjs';

const tick$ = new ConnectableObservable(
  timer(1000),
  () => new Subject()
);
tick$.connect();

multicast

multicast with subject factory

import { timer, multicast, Subject, ConnectableObservable } from 'rxjs';

const tick$ = timer(1000).pipe(
  multicast(() => new Subject())
) as ConnectableObservable<number>;
tick$.connect();

multicast with subject instance

import { timer, multicast, Subject, ConnectableObservable } from 'rxjs';

const tick$ = timer(1000).pipe(
  multicast(new Subject())
) as ConnectableObservable<number>;
tick$.connect();

multicast with refCount

import { timer, multicast, Subject, refCount } from 'rxjs';

const tick$ = timer(1000).pipe(
  multicast(() => new Subject()),
  refCount()
);

multicast with selector

import { timer, multicast, Subject, combineLatest } from 'rxjs';

const tick$ = timer(1000).pipe(
  multicast(
    () => new Subject(),
    source => combineLatest([source, source])
  )
);

publish Variants

publish

import { timer, publish, ConnectableObservable } from 'rxjs';

const tick$ = timer(1000).pipe(
  publish()
) as ConnectableObservable<number>;
tick$.connect();

publishBehavior

import { timer, publishBehavior, ConnectableObservable } from 'rxjs';

const tick$ = timer(1000).pipe(
  publishBehavior(0)
) as ConnectableObservable<number>;
tick$.connect();

publishLast

import { timer, publishLast, ConnectableObservable } from 'rxjs';

const tick$ = timer(1000).pipe(
  publishLast()
) as ConnectableObservable<number>;
tick$.connect();

publishReplay

import { timer, publishReplay, ConnectableObservable } from 'rxjs';

const tick$ = timer(1000).pipe(
  publishReplay(2)
) as ConnectableObservable<number>;
tick$.connect();

refCount

import { timer, publish, refCount } from 'rxjs';

const tick$ = timer(1000).pipe(
  publish(),
  refCount()
);

Scheduler Argument

Deprecated in v6.5, will be removed in v8. Use scheduled() function instead of scheduler arguments.

Affected Operators

from, of, merge, concat
startWith, endWith
combineLatest

Migration to scheduled

of and from

import { of, asyncScheduler } from 'rxjs';

of(1, 2, 3, asyncScheduler).subscribe(console.log);

import { from, asyncScheduler } from 'rxjs';

from([1, 2, 3], asyncScheduler).subscribe(console.log);

concat

import { concat, of, asyncScheduler } from 'rxjs';

concat(
  of('hello'),
  of('world'),
  asyncScheduler
).subscribe(console.log);

merge

import { merge, of, asyncScheduler } from 'rxjs';

merge(
  of(1, 2),
  of(3, 4),
  asyncScheduler
).subscribe(console.log);

combineLatest

import { combineLatest, of, asyncScheduler } from 'rxjs';

combineLatest(
  of('hello'),
  of('world'),
  asyncScheduler
).subscribe(console.log);

ResultSelector Parameter

Deprecated in v6.0, will be removed in v8. Use map operator instead of resultSelector parameter.

Why It Was Deprecated

Increases bundle size for every operator
Can cause memory pressure by retaining values
Same functionality available via map

Affected Operators

concatMap, concatMapTo
exhaustMap
mergeMap, mergeMapTo
switchMap, switchMapTo

Migration Examples

import { fromEvent, switchMap, interval } from 'rxjs';

fromEvent(document, 'click').pipe(
  switchMap(
    () => interval(1000),
    (outer, inner) => inner + 1 // resultSelector
  )
).subscribe(console.log);

import { of, mergeMap } from 'rxjs';

of(1, 2, 3).pipe(
  mergeMap(
    x => of(x * 10),
    (outer, inner) => ({ outer, inner }) // resultSelector
  )
).subscribe(console.log);

Array Arguments

Deprecated in v6.5. Pass arrays or objects instead of multiple arguments.

Affected Operators

combineLatest
forkJoin

Migration Examples

import { forkJoin, of } from 'rxjs';

const odd$ = of(1, 3, 5);
const even$ = of(2, 4, 6);

forkJoin(odd$, even$).subscribe(console.log);

import { combineLatest, of } from 'rxjs';

combineLatest(
  of(1),
  of('a'),
  of(true)
).subscribe(console.log);

Deprecated Operators

concat, merge, zip, race (Pipeable)

The pipeable versions of concat, merge, zip, and race are deprecated. Use the new -With variants.

import { of } from 'rxjs';
import { concat, merge, zip, race } from 'rxjs/operators';

of(1).pipe(concat(of(2))).subscribe();
of(1).pipe(merge(of(2))).subscribe();
of(1).pipe(zip(of(2))).subscribe();
of(1).pipe(race(of(2))).subscribe();

Migration Timeline

RxJS v6.4 (2019)

Subscribe arguments deprecated

RxJS v6.5 (2019)

Scheduler arguments deprecated
Array arguments pattern introduced
ResultSelector deprecated

RxJS v7 (2021)

All v6 deprecations still functional
toPromise() deprecated
Multicasting APIs deprecated
New replacement APIs introduced

RxJS v8 (Future)

All deprecated APIs will be removed

Quick Reference

Deprecated API	Replacement	Version
`toPromise()`	`firstValueFrom()` / `lastValueFrom()`	v7 → v8
`subscribe(fn, fn, fn)`	`subscribe({ next, error, complete })`	v6.4 → v8
`multicast()`	`connectable()` / `share()`	v7 → v8
`publish()`	`connectable()` / `share()`	v7 → v8
`publishBehavior()`	`connectable()` with `BehaviorSubject`	v7 → v8
`publishLast()`	`connectable()` with `AsyncSubject`	v7 → v8
`publishReplay()`	`connectable()` / `shareReplay()`	v7 → v8
`refCount()`	`share()`	v7 → v8
`of(..., scheduler)`	`scheduled([...], scheduler)`	v6.5 → v8
`resultSelector` parameter	`map()` operator	v6.0 → v8
`combineLatest(a, b)`	`combineLatest([a, b])`	v6.5 → v8
`concat` operator	`concatWith`	v7 → v8
`merge` operator	`mergeWith`	v7 → v8
`zip` operator	`zipWith`	v7 → v8
`race` operator	`raceWith`	v7 → v8

Additional Resources

Migration Guide - Complete migration instructions
Breaking Changes - All breaking changes in v7
RxJS Changelog - Official changelog

Get Started

Core Concepts

Guides

Migration

Deprecated APIs

Deprecated APIs in RxJS v7

Promise Conversion

toPromise()

Migration to lastValueFrom

Migration to firstValueFrom

Handling Empty Observables

Multiple Function Arguments

Why This Was Deprecated

Migration Examples

tap Operator

Multicasting APIs

ConnectableObservable

multicast

publish Variants

refCount

Scheduler Argument

Affected Operators

Migration to scheduled

ResultSelector Parameter

Why It Was Deprecated

Affected Operators

Migration Examples

Array Arguments

Affected Operators

Migration Examples

Deprecated Operators

concat, merge, zip, race (Pipeable)

Migration Timeline

Quick Reference

Additional Resources

Get Started

Core Concepts

Guides

Migration

​Deprecated APIs in RxJS v7

​Promise Conversion

​toPromise()

​Migration to lastValueFrom

​Migration to firstValueFrom

​Handling Empty Observables

​Subscribe Arguments

​Multiple Function Arguments

​Why This Was Deprecated

​Migration Examples

​tap Operator

​Multicasting APIs

​ConnectableObservable

​multicast

​publish Variants

​refCount

​Scheduler Argument

​Affected Operators

​Migration to scheduled

​ResultSelector Parameter

​Why It Was Deprecated

​Affected Operators

​Migration Examples

​Array Arguments

​Affected Operators

​Migration Examples

​Deprecated Operators

​concat, merge, zip, race (Pipeable)

​Migration Timeline

​Quick Reference

​Additional Resources

Deprecated APIs in RxJS v7

Promise Conversion

toPromise()

Migration to lastValueFrom

Migration to firstValueFrom

Handling Empty Observables

Subscribe Arguments

Multiple Function Arguments

Why This Was Deprecated

Migration Examples

tap Operator

Multicasting APIs

ConnectableObservable

multicast

publish Variants

refCount

Scheduler Argument

Affected Operators

Migration to scheduled

ResultSelector Parameter

Why It Was Deprecated

Affected Operators

Migration Examples

Array Arguments

Affected Operators

Migration Examples

Deprecated Operators

concat, merge, zip, race (Pipeable)

Migration Timeline

Quick Reference

Additional Resources