Subscribing with multiple parameters in RxJS

Question

Subscribing with multiple parameters in RxJS

I am facing a dilemma with two observables that I need to combine and use in subscribe, where I want the flexibility to either use both arguments or only one. I have experimented with .ForkJoin, .merge, .concat but haven't been able to achieve the desired behavior.

For instance:

obs1: Observable<int>;
obs2: Observable<Boolean>;

save(): Observable<any> {
   return obs1.concat(obs2);
}

When utilizing this function:

service.save().subscribe((first, second) => {
    console.log(first); // int e.g. 1000
    console.log(second); // Boolean, e.g. true
});

or

service.save().subscribe((first) => {
    console.log(first); // int e.g. 1000
});

Is there a way to achieve this specific behavior?

I hope someone can provide assistance!

EDIT:

In my particular situation obs1<int> and obs2<bool> represent two distinct post requests: obs1<int> is the actual save operation and obs2<bool> checks if another service is active.

The value of obs1<int> is necessary for refreshing the page after the request is completed, while the value of obs2<bool> is required for displaying a message if the service is running - regardless of obs1<int>.

If obs2<bool> emits before obs1<int>, it's not an issue as the message will be displayed before the reload. However, if obs1<int> emits first, the page will reload and the message may not appear.

I mention this because the provided answers yield different outcomes based on whether the values are emitted before or after completion of the other observable, impacting the overall scenario.

javascript angular typescript rxjs

Answer 1

Answer №1

There are various operators that can achieve this:

Merge

This operator merges the latest values emitted by both observables, as illustrated in the marble diagram:

obs1: Observable<int>;
obs2: Observable<Boolean>;

combineAndSave(): Observable<any> {
   return merge(obs1, obs2);
}

combineAndSave().subscribe((value1, value2) => { 
   // perform logic here
});

Concat

The Concat operator will wait for both observables to emit values sequentially before emitting them.

obs1: Observable<int>;
obs2: Observable<Boolean>;

concatAndSave(): Observable<any> {
   return concat(obs1, obs2);
}

concatAndSave().subscribe((values) => { 
   // Note Values = [value1, value2]
   // Perform logic
});

Alternatively, if you prefer to destructure with an array

concatAndSave().subscribe(([value1, value2]) => {
   // Perform logic
});

Join

The Join operator combines the last values emitted by the observables, omitting any values without a corresponding pair from the other observable.

saveResult: obs1.pipe(joinWith(secondSource))

saveResult().subscribe(([value1, value2]) => {
    // Implement your logic here
});

Answer 2

There are various operators that can achieve this:

Merge

This operator merges the latest values emitted by both observables, as illustrated in the marble diagram:

obs1: Observable<int>;
obs2: Observable<Boolean>;

combineAndSave(): Observable<any> {
   return merge(obs1, obs2);
}

combineAndSave().subscribe((value1, value2) => { 
   // perform logic here
});

Concat

The Concat operator will wait for both observables to emit values sequentially before emitting them.

obs1: Observable<int>;
obs2: Observable<Boolean>;

concatAndSave(): Observable<any> {
   return concat(obs1, obs2);
}

concatAndSave().subscribe((values) => { 
   // Note Values = [value1, value2]
   // Perform logic
});

Alternatively, if you prefer to destructure with an array

concatAndSave().subscribe(([value1, value2]) => {
   // Perform logic
});

Join

The Join operator combines the last values emitted by the observables, omitting any values without a corresponding pair from the other observable.

saveResult: obs1.pipe(joinWith(secondSource))

saveResult().subscribe(([value1, value2]) => {
    // Implement your logic here
});

Answer 3

Answer №2

If you want to achieve this, you can use the 'forkJoin' method. This allows you to make parallel calls and then take action based on the response of either one.

let numberSource = Rx.Observable.of(100);
let booleanSource = Rx.Observable.of(true);

Rx.Observable.forkJoin(
  numberSource,
  booleanSource
).subscribe( ([numberResp, booleanResp]) => {
  if (numberResp) {
    console.log(numberResp);
    // perform specific task
  } else if (booleanResp) {
    console.log(booleanResp);
    // perform specific task
  }
});

Answer 4

If you want to achieve this, you can use the 'forkJoin' method. This allows you to make parallel calls and then take action based on the response of either one.

let numberSource = Rx.Observable.of(100);
let booleanSource = Rx.Observable.of(true);

Rx.Observable.forkJoin(
  numberSource,
  booleanSource
).subscribe( ([numberResp, booleanResp]) => {
  if (numberResp) {
    console.log(numberResp);
    // perform specific task
  } else if (booleanResp) {
    console.log(booleanResp);
    // perform specific task
  }
});

Answer 5

Answer №3

You have the option to utilize the zip static method in place of the concat operator.

save(): Observable<any> {
   return zip(obs1, obs2);
}

Subsequently, you can implement it like so:

service.save().subscribe((x) => {
    console.log(x[0]); // for example, an integer like 1000
    console.log(x[1]); // Boolean value, e.g. true
});

Answer 6

You have the option to utilize the zip static method in place of the concat operator.

save(): Observable<any> {
   return zip(obs1, obs2);
}

Subsequently, you can implement it like so:

service.save().subscribe((x) => {
    console.log(x[0]); // for example, an integer like 1000
    console.log(x[1]); // Boolean value, e.g. true
});

Answer 7

Answer №4

The operator you choose will vary depending on the specific situation you're dealing with.

One possibility is to utilize the combineLatest operator - check out the documentation for more details:

source1$: Observable<number>;
source2$: Observable<Boolean>;
combinedSource$ = combineLatest(source1$, source2$);

combinedSource$.subscribe(([data1, data2]) => {
  console.log(data1);
  console.log(data2);
})

Answer 8

The operator you choose will vary depending on the specific situation you're dealing with.

One possibility is to utilize the combineLatest operator - check out the documentation for more details:

source1$: Observable<number>;
source2$: Observable<Boolean>;
combinedSource$ = combineLatest(source1$, source2$);

combinedSource$.subscribe(([data1, data2]) => {
  console.log(data1);
  console.log(data2);
})

Answer 9

Answer №5

When dealing with streams of data, it's important to choose the right method to handle emissions. Concat and Merge emit events in different ways, but if you want both values at the same time, forkJoin, zip, and combineLatest are the way to go. These methods will give you the values in a single stream event, unlike concat and merge which emit one after the other.

Zip combines all items emitted by observables in sequence, while combineLatest emits whenever either observable emits a value. On the other hand, forkJoin only emits once when all items inside have completed. This can be useful when you're "saving" since it guarantees proper completion and avoids memory leaks. It is a safer option for handling single emissions.

To access the values from these emissions, using TypeScript syntax like this example can help:

obs1: Observable<int>;
obs2: Observable<Boolean>;

save(): Observable<any> {
   return forkJoin(obs1, obs2);
}

service.save().subscribe(([first, second]) => {
    console.log(first); // int e.g. 1000
    console.log(second); // Boolean, e.g. true
});

While TypeScript provides ways to access array items, remember that subscribe functions only accept a single argument. Choose the method that best fits your needs based on the type of emissions you expect from your observables.

Answer 10

When dealing with streams of data, it's important to choose the right method to handle emissions. Concat and Merge emit events in different ways, but if you want both values at the same time, forkJoin, zip, and combineLatest are the way to go. These methods will give you the values in a single stream event, unlike concat and merge which emit one after the other.

Zip combines all items emitted by observables in sequence, while combineLatest emits whenever either observable emits a value. On the other hand, forkJoin only emits once when all items inside have completed. This can be useful when you're "saving" since it guarantees proper completion and avoids memory leaks. It is a safer option for handling single emissions.

To access the values from these emissions, using TypeScript syntax like this example can help:

obs1: Observable<int>;
obs2: Observable<Boolean>;

save(): Observable<any> {
   return forkJoin(obs1, obs2);
}

service.save().subscribe(([first, second]) => {
    console.log(first); // int e.g. 1000
    console.log(second); // Boolean, e.g. true
});

While TypeScript provides ways to access array items, remember that subscribe functions only accept a single argument. Choose the method that best fits your needs based on the type of emissions you expect from your observables.

Subscribing with multiple parameters in RxJS

Answer №1

Merge

Concat

Join

Answer №2

Answer №3

Answer №4

Answer №5

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