What is the best way to ensure an observable has been updated before proceeding with additional code execution?

Question

What is the best way to ensure an observable has been updated before proceeding with additional code execution?

Is an observable the best choice for providing live updates of a variable's value to another class? I have a loop in my service class that looks like this:

elements.forEach(element => {
  doStuff();
  this.numberSubject.next(valueFromDoStuff);
})

In my component class, I am subscribing to the observable:

numberSubjectObservable.subscribe(result => {
  this.value = result
}

I want the loop to pause until my Angular component is updated with the newest value from the subscription. Currently, it waits until the end before rendering the final value.

javascript angular typescript angular2-observables

Answer 1

Answer №1

If you're unsure whether your doStuff() function is synchronous or asynchronous, it could affect how updates are displayed in your progress bar. With synchronous functions, changes happen instantly and only the final value is visible.

For asynchronous functions, using forEach may not be suitable. You can check out more information on this at this link.

A helpful demo has been prepared for better understanding. The demo includes a button for triggering synchronous iteration and another for asynchronous iteration.

To simulate an async doStuff process:

private async asyncDoStuff(element: number): Promise<number>{
  console.log('running async doStuff with element: ' + element);
  return new Promise(resolve => {
   setTimeout(resolve, 1000);
  }).then(()=>{return this.doStuff(element);});
}

Additionally, looping through your array to observe updates with a 1-second delay:

public async asyncIterate(){
  let newElement = 0;
  for (const element of this.elements){
  newElement = await this.asyncDoStuff(element);
  console.log('newElement: ' + newElement);
  this.numberAsyncSubject.next(newElement);
  }
}

Answer 2

If you're unsure whether your doStuff() function is synchronous or asynchronous, it could affect how updates are displayed in your progress bar. With synchronous functions, changes happen instantly and only the final value is visible.

For asynchronous functions, using forEach may not be suitable. You can check out more information on this at this link.

A helpful demo has been prepared for better understanding. The demo includes a button for triggering synchronous iteration and another for asynchronous iteration.

To simulate an async doStuff process:

private async asyncDoStuff(element: number): Promise<number>{
  console.log('running async doStuff with element: ' + element);
  return new Promise(resolve => {
   setTimeout(resolve, 1000);
  }).then(()=>{return this.doStuff(element);});
}

Additionally, looping through your array to observe updates with a 1-second delay:

public async asyncIterate(){
  let newElement = 0;
  for (const element of this.elements){
  newElement = await this.asyncDoStuff(element);
  console.log('newElement: ' + newElement);
  this.numberAsyncSubject.next(newElement);
  }
}

Answer 3

Answer №2

It seems like you're not quite clear on your intentions here, but if you're waiting for this.value to match the numberSubjectObservable result, you can utilize an async method with the following approach:

You have the option to modify this

numberSubjectObservable.subscribe(result => {
  this.value = result
}

to this

this.value = await numberSubjectObservable.toPromise();

Answer 4

It seems like you're not quite clear on your intentions here, but if you're waiting for this.value to match the numberSubjectObservable result, you can utilize an async method with the following approach:

You have the option to modify this

numberSubjectObservable.subscribe(result => {
  this.value = result
}

to this

this.value = await numberSubjectObservable.toPromise();

What is the best way to ensure an observable has been updated before proceeding with additional code execution?

Answer №1

Answer №2

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