How to convert an Observable into a BehaviorSubject?
0
I'm trying to convert an Observable into a BehaviorSubject. Like this:
a$ = new Observable()
b$ = BehaviorSubject.create(new BehaviorSubject(123), a$)
// 🔴
I have also tried:
a$ = new Observable()
b$ = new BehaviorSubject(a$, 123)
// 🔴
And:
a$ = new Observable()
b$ = a$.asBehaviorSubject(123)
// 🔴
And:
a$ = new Observable()
b$ = a$.pipe(
toBehaviorSubject(123)
)
// 🔴
But none of these works. For now I have to implement like this:
a$ = new Observable()
b$ = new BehaviorSubject(123)
a$.subscribe(b$)
// 🔵
This would be a little bit ugly in a class:
class Foo() {
a$ = new Observable() // Actually, a$ is more complicated than this.
b$ = new BehaviorSubject(123)
constructor() {
this.a$.subscribe(this.b$)
}
}
So, is there a simpler way to convert a Observable to a BehaviorSubject without using class constructor?
This is my real case:
export class Foo {
autoCompleteItems$ = new BehaviorSubject<string>(null)
autoCompleteSelected$ = new BehaviorSubject<number>(-1)
autoCompleteSelectedChange$ = new Subject<'up'|'down'>()
constructor() {
this.autoCompleteItems$.pipe(
switchMap((items) => {
if (!items) return EMPTY
return this.autoCompleteSelectedChange$.pipe(
startWith('down'),
scan<any, number>((acc, value) => {
if (value === 'up') {
if (acc <= 0) {
return items.length - 1
} else {
return acc - 1
}
} else {
if (acc >= items.length - 1) {
return 0
} else {
return acc + 1
}
}
}, -1)
)
})
).subscribe(this.autoCompleteSelected$)
}
doAutoComplete = () => {
const item = this.autoCompleteItems$.value[this.autoCompleteSelected$.value]
// do something with `item`
}
}
javascript typescript rxjs observable behaviorsubject
asked Nov 19 at 9:57
awmleer
4472515
|
show 1 more comment
0
I'm trying to convert an Observable into a BehaviorSubject. Like this:
a$ = new Observable()
b$ = BehaviorSubject.create(new BehaviorSubject(123), a$)
// 🔴
I have also tried:
a$ = new Observable()
b$ = new BehaviorSubject(a$, 123)
// 🔴
And:
a$ = new Observable()
b$ = a$.asBehaviorSubject(123)
// 🔴
And:
a$ = new Observable()
b$ = a$.pipe(
toBehaviorSubject(123)
)
// 🔴
But none of these works. For now I have to implement like this:
a$ = new Observable()
b$ = new BehaviorSubject(123)
a$.subscribe(b$)
// 🔵
This would be a little bit ugly in a class:
class Foo() {
a$ = new Observable() // Actually, a$ is more complicated than this.
b$ = new BehaviorSubject(123)
constructor() {
this.a$.subscribe(this.b$)
}
}
So, is there a simpler way to convert a Observable to a BehaviorSubject without using class constructor?
This is my real case:
export class Foo {
autoCompleteItems$ = new BehaviorSubject<string>(null)
autoCompleteSelected$ = new BehaviorSubject<number>(-1)
autoCompleteSelectedChange$ = new Subject<'up'|'down'>()
constructor() {
this.autoCompleteItems$.pipe(
switchMap((items) => {
if (!items) return EMPTY
return this.autoCompleteSelectedChange$.pipe(
startWith('down'),
scan<any, number>((acc, value) => {
if (value === 'up') {
if (acc <= 0) {
return items.length - 1
} else {
return acc - 1
}
} else {
if (acc >= items.length - 1) {
return 0
} else {
return acc + 1
}
}
}, -1)
)
})
).subscribe(this.autoCompleteSelected$)
}
doAutoComplete = () => {
const item = this.autoCompleteItems$.value[this.autoCompleteSelected$.value]
// do something with `item`
}
}
javascript typescript rxjs observable behaviorsubject
asked Nov 19 at 9:57
awmleer
4472515
1
What is the usecase for this? You can typically use justmerge. Usingsubscribeis the most Rx way I think.
– martin
Nov 19 at 10:00
Which is the reason you want to convert an Observable to a BehaviourSubject? Is it because you want to have access to the last value? If this is the case you can look atshareReplyor a sequence ofpublishReplayandrefCount
– Picci
Nov 19 at 10:08
@Picci Yes. I want to have access to the latest value. Thanks for advise! I'm going to have a look on these APIs.
– awmleer
Nov 19 at 10:11
@Picci Actually I want to write something likeb$.valueorb$.getValue().
– awmleer
Nov 19 at 10:16
1
With subjects,valueandgetValueare code smells and are best avoided.
– cartant
Nov 19 at 13:01
|
show 1 more comment
0
0
0
I'm trying to convert an Observable into a BehaviorSubject. Like this:
a$ = new Observable()
b$ = BehaviorSubject.create(new BehaviorSubject(123), a$)
// 🔴
I have also tried:
a$ = new Observable()
b$ = new BehaviorSubject(a$, 123)
// 🔴
And:
a$ = new Observable()
b$ = a$.asBehaviorSubject(123)
// 🔴
And:
a$ = new Observable()
b$ = a$.pipe(
toBehaviorSubject(123)
)
// 🔴
But none of these works. For now I have to implement like this:
a$ = new Observable()
b$ = new BehaviorSubject(123)
a$.subscribe(b$)
// 🔵
This would be a little bit ugly in a class:
class Foo() {
a$ = new Observable() // Actually, a$ is more complicated than this.
b$ = new BehaviorSubject(123)
constructor() {
this.a$.subscribe(this.b$)
}
}
So, is there a simpler way to convert a Observable to a BehaviorSubject without using class constructor?
This is my real case:
export class Foo {
autoCompleteItems$ = new BehaviorSubject<string>(null)
autoCompleteSelected$ = new BehaviorSubject<number>(-1)
autoCompleteSelectedChange$ = new Subject<'up'|'down'>()
constructor() {
this.autoCompleteItems$.pipe(
switchMap((items) => {
if (!items) return EMPTY
return this.autoCompleteSelectedChange$.pipe(
startWith('down'),
scan<any, number>((acc, value) => {
if (value === 'up') {
if (acc <= 0) {
return items.length - 1
} else {
return acc - 1
}
} else {
if (acc >= items.length - 1) {
return 0
} else {
return acc + 1
}
}
}, -1)
)
})
).subscribe(this.autoCompleteSelected$)
}
doAutoComplete = () => {
const item = this.autoCompleteItems$.value[this.autoCompleteSelected$.value]
// do something with `item`
}
}
javascript typescript rxjs observable behaviorsubject
asked Nov 19 at 9:57
awmleer
4472515
I'm trying to convert an Observable into a BehaviorSubject. Like this:
a$ = new Observable()
b$ = BehaviorSubject.create(new BehaviorSubject(123), a$)
// 🔴
I have also tried:
a$ = new Observable()
b$ = new BehaviorSubject(a$, 123)
// 🔴
And:
a$ = new Observable()
b$ = a$.asBehaviorSubject(123)
// 🔴
And:
a$ = new Observable()
b$ = a$.pipe(
toBehaviorSubject(123)
)
// 🔴
But none of these works. For now I have to implement like this:
a$ = new Observable()
b$ = new BehaviorSubject(123)
a$.subscribe(b$)
// 🔵
This would be a little bit ugly in a class:
class Foo() {
a$ = new Observable() // Actually, a$ is more complicated than this.
b$ = new BehaviorSubject(123)
constructor() {
this.a$.subscribe(this.b$)
}
}
So, is there a simpler way to convert a Observable to a BehaviorSubject without using class constructor?
This is my real case:
export class Foo {
autoCompleteItems$ = new BehaviorSubject<string>(null)
autoCompleteSelected$ = new BehaviorSubject<number>(-1)
autoCompleteSelectedChange$ = new Subject<'up'|'down'>()
constructor() {
this.autoCompleteItems$.pipe(
switchMap((items) => {
if (!items) return EMPTY
return this.autoCompleteSelectedChange$.pipe(
startWith('down'),
scan<any, number>((acc, value) => {
if (value === 'up') {
if (acc <= 0) {
return items.length - 1
} else {
return acc - 1
}
} else {
if (acc >= items.length - 1) {
return 0
} else {
return acc + 1
}
}
}, -1)
)
})
).subscribe(this.autoCompleteSelected$)
}
doAutoComplete = () => {
const item = this.autoCompleteItems$.value[this.autoCompleteSelected$.value]
// do something with `item`
}
}
javascript typescript rxjs observable behaviorsubject
javascript typescript rxjs observable behaviorsubject
asked Nov 19 at 9:57
awmleer
4472515
asked Nov 19 at 9:57
awmleer
4472515
edited Nov 19 at 10:16
asked Nov 19 at 9:57
awmleer
4472515
asked Nov 19 at 9:57
awmleer
4472515
asked Nov 19 at 9:57
awmleer
4472515
4472515
1
What is the usecase for this? You can typically use justmerge. Usingsubscribeis the most Rx way I think.
– martin
Nov 19 at 10:00
Which is the reason you want to convert an Observable to a BehaviourSubject? Is it because you want to have access to the last value? If this is the case you can look atshareReplyor a sequence ofpublishReplayandrefCount
– Picci
Nov 19 at 10:08
@Picci Yes. I want to have access to the latest value. Thanks for advise! I'm going to have a look on these APIs.
– awmleer
Nov 19 at 10:11
@Picci Actually I want to write something likeb$.valueorb$.getValue().
– awmleer
Nov 19 at 10:16
1
With subjects,valueandgetValueare code smells and are best avoided.
– cartant
Nov 19 at 13:01
|
show 1 more comment
1
What is the usecase for this? You can typically use justmerge. Usingsubscribeis the most Rx way I think.
– martin
Nov 19 at 10:00
Which is the reason you want to convert an Observable to a BehaviourSubject? Is it because you want to have access to the last value? If this is the case you can look atshareReplyor a sequence ofpublishReplayandrefCount
– Picci
Nov 19 at 10:08
@Picci Yes. I want to have access to the latest value. Thanks for advise! I'm going to have a look on these APIs.
– awmleer
Nov 19 at 10:11
@Picci Actually I want to write something likeb$.valueorb$.getValue().
– awmleer
Nov 19 at 10:16
1
With subjects,valueandgetValueare code smells and are best avoided.
– cartant
Nov 19 at 13:01
1
1
What is the usecase for this? You can typically use just
merge. Using subscribe is the most Rx way I think.– martin
Nov 19 at 10:00
What is the usecase for this? You can typically use just
merge. Using subscribe is the most Rx way I think.– martin
Nov 19 at 10:00
Which is the reason you want to convert an Observable to a BehaviourSubject? Is it because you want to have access to the last value? If this is the case you can look at
shareReply or a sequence of publishReplay and refCount– Picci
Nov 19 at 10:08
Which is the reason you want to convert an Observable to a BehaviourSubject? Is it because you want to have access to the last value? If this is the case you can look at
shareReply or a sequence of publishReplay and refCount– Picci
Nov 19 at 10:08
@Picci Yes. I want to have access to the latest value. Thanks for advise! I'm going to have a look on these APIs.
– awmleer
Nov 19 at 10:11
@Picci Yes. I want to have access to the latest value. Thanks for advise! I'm going to have a look on these APIs.
– awmleer
Nov 19 at 10:11
@Picci Actually I want to write something like
b$.value or b$.getValue().– awmleer
Nov 19 at 10:16
@Picci Actually I want to write something like
b$.value or b$.getValue().– awmleer
Nov 19 at 10:16
1
1
With subjects,
value and getValue are code smells and are best avoided.– cartant
Nov 19 at 13:01
With subjects,
value and getValue are code smells and are best avoided.– cartant
Nov 19 at 13:01
|
show 1 more comment
1 Answer
1
active
oldest
votes
0
I have pretty concerns about the use case too. But here it comes a solution, feel free vote down as long you leave feedback too. Since BehaviourSubject and any other Subject are Observables,
import { BehaviorSubject, from } from 'rxjs';
import { map, mergeMap } from 'rxjs/operators';
const source$ = from([1,2,3,4,5,6,7,8,9]);
const bs = new BehaviorSubject('start')
.pipe(
mergeMap(() => source$)
);
bs.subscribe(console.log);
edited Nov 22 at 12:39
awmleer
4472515
answered Nov 20 at 5:07
Luillyfe
1,77332331
1
Thanks for answering! Butbsis still an observable andbs.valueis undefined.😥
– awmleer
Nov 22 at 12:14
add a comment |
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1 Answer
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oldest
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1 Answer
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active
oldest
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oldest
votes
active
oldest
votes
0
I have pretty concerns about the use case too. But here it comes a solution, feel free vote down as long you leave feedback too. Since BehaviourSubject and any other Subject are Observables,
import { BehaviorSubject, from } from 'rxjs';
import { map, mergeMap } from 'rxjs/operators';
const source$ = from([1,2,3,4,5,6,7,8,9]);
const bs = new BehaviorSubject('start')
.pipe(
mergeMap(() => source$)
);
bs.subscribe(console.log);
edited Nov 22 at 12:39
awmleer
4472515
answered Nov 20 at 5:07
Luillyfe
1,77332331
1
Thanks for answering! Butbsis still an observable andbs.valueis undefined.😥
– awmleer
Nov 22 at 12:14
add a comment |
0
I have pretty concerns about the use case too. But here it comes a solution, feel free vote down as long you leave feedback too. Since BehaviourSubject and any other Subject are Observables,
import { BehaviorSubject, from } from 'rxjs';
import { map, mergeMap } from 'rxjs/operators';
const source$ = from([1,2,3,4,5,6,7,8,9]);
const bs = new BehaviorSubject('start')
.pipe(
mergeMap(() => source$)
);
bs.subscribe(console.log);
edited Nov 22 at 12:39
awmleer
4472515
answered Nov 20 at 5:07
Luillyfe
1,77332331
1
Thanks for answering! Butbsis still an observable andbs.valueis undefined.😥
– awmleer
Nov 22 at 12:14
add a comment |
0
0
0
I have pretty concerns about the use case too. But here it comes a solution, feel free vote down as long you leave feedback too. Since BehaviourSubject and any other Subject are Observables,
import { BehaviorSubject, from } from 'rxjs';
import { map, mergeMap } from 'rxjs/operators';
const source$ = from([1,2,3,4,5,6,7,8,9]);
const bs = new BehaviorSubject('start')
.pipe(
mergeMap(() => source$)
);
bs.subscribe(console.log);
edited Nov 22 at 12:39
awmleer
4472515
answered Nov 20 at 5:07
Luillyfe
1,77332331
I have pretty concerns about the use case too. But here it comes a solution, feel free vote down as long you leave feedback too. Since BehaviourSubject and any other Subject are Observables,
import { BehaviorSubject, from } from 'rxjs';
import { map, mergeMap } from 'rxjs/operators';
const source$ = from([1,2,3,4,5,6,7,8,9]);
const bs = new BehaviorSubject('start')
.pipe(
mergeMap(() => source$)
);
bs.subscribe(console.log);
edited Nov 22 at 12:39
awmleer
4472515
answered Nov 20 at 5:07
Luillyfe
1,77332331
edited Nov 22 at 12:39
awmleer
4472515
edited Nov 22 at 12:39
awmleer
4472515
edited Nov 22 at 12:39
awmleer
4472515
4472515
answered Nov 20 at 5:07
Luillyfe
1,77332331
answered Nov 20 at 5:07
Luillyfe
1,77332331
answered Nov 20 at 5:07
Luillyfe
1,77332331
1,77332331
1
Thanks for answering! Butbsis still an observable andbs.valueis undefined.😥
– awmleer
Nov 22 at 12:14
add a comment |
1
Thanks for answering! Butbsis still an observable andbs.valueis undefined.😥
– awmleer
Nov 22 at 12:14
1
1
Thanks for answering! But
bs is still an observable and bs.value is undefined.😥– awmleer
Nov 22 at 12:14
Thanks for answering! But
bs is still an observable and bs.value is undefined.😥– awmleer
Nov 22 at 12:14
add a comment |
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1
What is the usecase for this? You can typically use just
merge. Usingsubscribeis the most Rx way I think.– martin
Nov 19 at 10:00
Which is the reason you want to convert an Observable to a BehaviourSubject? Is it because you want to have access to the last value? If this is the case you can look at
shareReplyor a sequence ofpublishReplayandrefCount– Picci
Nov 19 at 10:08
@Picci Yes. I want to have access to the latest value. Thanks for advise! I'm going to have a look on these APIs.
– awmleer
Nov 19 at 10:11
@Picci Actually I want to write something like
b$.valueorb$.getValue().– awmleer
Nov 19 at 10:16
1
With subjects,
valueandgetValueare code smells and are best avoided.– cartant
Nov 19 at 13:01