What are the benefits of pairing Observables with async/await for asynchronous operations?

Question

What are the benefits of pairing Observables with async/await for asynchronous operations?

Utilizing Angular 2 common HTTP that returns an Observable presents a challenge with nested Observable calls causing code complexity:

this.serviceA.get().subscribe((res1: any) => {
   this.serviceB.get(res1).subscribe((res2: any) => {
       this.serviceC.get(res2).subscribe((res3: any) => {

       })
   })
})

Seeking to use async/await to simplify the code structure, but facing the limitation that async/await only works with Promises. Converting Observables to Promises is typically not recommended. How should this be approached?

If possible, an example code snippet demonstrating the use of async/await to resolve this issue would be greatly appreciated! :D

javascript angular typescript promise observable

Answer 1

Answer №1

Sequencing Observables in Your Code

If you need to chain Observables in sequence, consider using the flatMap or switchMap operators. Here's an example:

this.serviceA.get()
  .flatMap((res1: any) => this.serviceB.get())
  .flatMap((res2: any) => this.serviceC.get())
  .subscribe( (res3: any) => { 
    .... 
  });

Chaining Observables in this way is a better practice than nesting, as it improves clarity and helps avoid callback hell that Observable and Promises were designed to prevent.

Additionally, consider using switchMap instead of flatMap to 'cancel' other requests if the first one emits a new value. This is useful when the first Observable is triggered by an event like a button click.

To start multiple requests simultaneously without waiting for each other, you can use forkJoin or zip. Check out the details in @Dan Macak's answer.

Combining Angular 'async' Pipe with Observables

In Angular, you can use the | async pipe in templates instead of subscribing to Observables in your component code to access emitted values.

Considering ES6 async/await and Promises

If you prefer using Promises over Observables, you can convert an Observable to a Promise using .toPromise() and then use async/await. However, it's recommended to stick with Observables for their additional features unless necessary.

Here's an example of using async/await with Promises:

// Warning: potential anti-pattern below
async myFunction() {
    const res1 = await this.serviceA.get().toPromise();
    const res2 = await this.serviceB.get().toPromise();
    const res3 = await this.serviceC.get().toPromise();
    // other operations with results
}

If you want to start requests simultaneously, consider using await Promise.all() for better efficiency.

async myFunction() {
    const promise1 = this.serviceA.get().toPromise();
    const promise2 = this.serviceB.get().toPromise();
    const promise3 = this.serviceC.get().toPromise();

    let res = await Promise.all([promise1, promise2, promise3]);

    // access results in res[0], res[1], res[2]
}

Answer 2

Sequencing Observables in Your Code

If you need to chain Observables in sequence, consider using the flatMap or switchMap operators. Here's an example:

this.serviceA.get()
  .flatMap((res1: any) => this.serviceB.get())
  .flatMap((res2: any) => this.serviceC.get())
  .subscribe( (res3: any) => { 
    .... 
  });

Chaining Observables in this way is a better practice than nesting, as it improves clarity and helps avoid callback hell that Observable and Promises were designed to prevent.

Additionally, consider using switchMap instead of flatMap to 'cancel' other requests if the first one emits a new value. This is useful when the first Observable is triggered by an event like a button click.

To start multiple requests simultaneously without waiting for each other, you can use forkJoin or zip. Check out the details in @Dan Macak's answer.

Combining Angular 'async' Pipe with Observables

In Angular, you can use the | async pipe in templates instead of subscribing to Observables in your component code to access emitted values.

Considering ES6 async/await and Promises

If you prefer using Promises over Observables, you can convert an Observable to a Promise using .toPromise() and then use async/await. However, it's recommended to stick with Observables for their additional features unless necessary.

Here's an example of using async/await with Promises:

// Warning: potential anti-pattern below
async myFunction() {
    const res1 = await this.serviceA.get().toPromise();
    const res2 = await this.serviceB.get().toPromise();
    const res3 = await this.serviceC.get().toPromise();
    // other operations with results
}

If you want to start requests simultaneously, consider using await Promise.all() for better efficiency.

async myFunction() {
    const promise1 = this.serviceA.get().toPromise();
    const promise2 = this.serviceB.get().toPromise();
    const promise3 = this.serviceC.get().toPromise();

    let res = await Promise.all([promise1, promise2, promise3]);

    // access results in res[0], res[1], res[2]
}

Answer 3

Answer №2

After @Pac0 has provided a comprehensive overview of the various solutions, I would like to offer a slightly different perspective.

Blending Promises and Observables

Personally, I lean towards avoiding mixing Promises and Observables when using async/await with Observables. Despite their superficial similarities, they are fundamentally distinct.

Promises are inherently asynchronous, while Observables may not be
Promises convey a single value, whereas Observables can emit 0, 1, or many values
Promises are limited in functionality, lacking features like cancellation, unlike Observables which are more versatile (e.g., managing multiple WebSocket connections)
They have different APIs

Utilizing Promises in Angular

Although there are scenarios where utilizing both is acceptable, particularly with Angular, it's advantageous to delve deeper into RxJS. This is due to:

Angular's API heavily relies on Observables (e.g., router, http...), aligning with RxJS enhances interoperability and capitalizes on RxJS's capabilities without the need for frequent Promise conversions
Angular's async pipe facilitates composing a seamless data flow within your application, allowing for streamlined manipulation of data from services to templates without interruption or manual handling

However, there are instances where using Promises can still be beneficial. For example, the clarity provided by Promises over Observables in specifying the type of data to be expected (single value, multiple values, or completion).

It's essential to strike a balance between Promises and Observables in your project. Promises are ideal for expressing completion status or sequential code execution with async/await, simplifying code. On the other hand, if advanced data management is required, Observables are more suitable.

Regarding Your Example

My suggestion is to embrace the capabilities of RxJS and Angular together. In your example, you can implement the code as follows:

this.result$ = Observable.forkJoin(
  this.serviceA.get(),
  this.serviceB.get(),
  this.serviceC.get()
);

this.result$.subscribe(([resA, resB, resC]) => ...)

By using forkJoin, you can handle multiple requests concurrently and receive the combined results efficiently. Alternatively, utilizing Observable.zip would yield similar results with a slight variation in behavior.

Edit: To address the need for the results of previous HTTP requests, consider implementing the flatMap approach outlined in @Pac0's answer.

Answer 4

After @Pac0 has provided a comprehensive overview of the various solutions, I would like to offer a slightly different perspective.

Blending Promises and Observables

Personally, I lean towards avoiding mixing Promises and Observables when using async/await with Observables. Despite their superficial similarities, they are fundamentally distinct.

Promises are inherently asynchronous, while Observables may not be
Promises convey a single value, whereas Observables can emit 0, 1, or many values
Promises are limited in functionality, lacking features like cancellation, unlike Observables which are more versatile (e.g., managing multiple WebSocket connections)
They have different APIs

Utilizing Promises in Angular

Although there are scenarios where utilizing both is acceptable, particularly with Angular, it's advantageous to delve deeper into RxJS. This is due to:

Angular's API heavily relies on Observables (e.g., router, http...), aligning with RxJS enhances interoperability and capitalizes on RxJS's capabilities without the need for frequent Promise conversions
Angular's async pipe facilitates composing a seamless data flow within your application, allowing for streamlined manipulation of data from services to templates without interruption or manual handling

However, there are instances where using Promises can still be beneficial. For example, the clarity provided by Promises over Observables in specifying the type of data to be expected (single value, multiple values, or completion).

It's essential to strike a balance between Promises and Observables in your project. Promises are ideal for expressing completion status or sequential code execution with async/await, simplifying code. On the other hand, if advanced data management is required, Observables are more suitable.

Regarding Your Example

My suggestion is to embrace the capabilities of RxJS and Angular together. In your example, you can implement the code as follows:

this.result$ = Observable.forkJoin(
  this.serviceA.get(),
  this.serviceB.get(),
  this.serviceC.get()
);

this.result$.subscribe(([resA, resB, resC]) => ...)

By using forkJoin, you can handle multiple requests concurrently and receive the combined results efficiently. Alternatively, utilizing Observable.zip would yield similar results with a slight variation in behavior.

Edit: To address the need for the results of previous HTTP requests, consider implementing the flatMap approach outlined in @Pac0's answer.

Answer 5

Answer №3

Due to the deprecation of toPromise in the year 2022, I would like to introduce an alternative way of using await with observables. This approach provides a much cleaner code structure compared to lengthy and complex rxjs pipes. It is especially beneficial for handling http requests where waiting for a single response before proceeding is essential.

Latest Update

Although my original solution is effective, rxjs now offers a similar function called firstValueFrom().

As mentioned in the documentation:

async function execute() {
  const source$ = interval(2000);
  const firstNumber = await firstValueFrom(source$);
  console.log(`The first number is ${firstNumber}`);
}

Initial Solution

If you have an observable, you can convert it into a promise, subscribe to it, and resolve the promise when the subscription emits.

getSomething(): Promise<any> {
    return new Promise((resolve, reject) => {
      this.http
        .get('www.myApi.com')
        .subscribe({
          next: (data) => resolve(data),
          error: (err) => reject(err),
        });
    });
  }

Now it is possible to await a response within an async function.

  async ngOnInit() {
    const data = await this.getSomething();
    //Do something with your data
  }

This method allows for intricate data operations while presenting a more readable code structure, especially for individuals not familiar with rxjs intricacies. For instance, handling three sequential http requests that depend on each other would appear as follows:

  async ngOnInit() {
    const first = await this.getFirst();
    const second = await this.getSecond(first);
    const third = await this.getThird(second);
  }

Answer 6

Due to the deprecation of toPromise in the year 2022, I would like to introduce an alternative way of using await with observables. This approach provides a much cleaner code structure compared to lengthy and complex rxjs pipes. It is especially beneficial for handling http requests where waiting for a single response before proceeding is essential.

Latest Update

Although my original solution is effective, rxjs now offers a similar function called firstValueFrom().

As mentioned in the documentation:

async function execute() {
  const source$ = interval(2000);
  const firstNumber = await firstValueFrom(source$);
  console.log(`The first number is ${firstNumber}`);
}

Initial Solution

If you have an observable, you can convert it into a promise, subscribe to it, and resolve the promise when the subscription emits.

getSomething(): Promise<any> {
    return new Promise((resolve, reject) => {
      this.http
        .get('www.myApi.com')
        .subscribe({
          next: (data) => resolve(data),
          error: (err) => reject(err),
        });
    });
  }

Now it is possible to await a response within an async function.

  async ngOnInit() {
    const data = await this.getSomething();
    //Do something with your data
  }

This method allows for intricate data operations while presenting a more readable code structure, especially for individuals not familiar with rxjs intricacies. For instance, handling three sequential http requests that depend on each other would appear as follows:

  async ngOnInit() {
    const first = await this.getFirst();
    const second = await this.getSecond(first);
    const third = await this.getThird(second);
  }

Answer 7

Answer №4

When dealing with streams, such as BehaviorSubject, observables are a great choice. However, for a single data call (e.g. http.get()), it's more efficient to make the service call itself asynchronous.

async getSomethingById(id: number): Promise<Something> {
    return await this.http.get<Something>(`api/things/${id}`).toPromise();
}

By doing this, you can simply call the function like this:

async someFunc(): Promise {
    console.log(await getSomethingById(1));
}

Although RxJS is powerful, using it for a basic API call may be excessive. Even if you need to manipulate the retrieved data, you can utilize RxJS operators within the getSomethingById function and return the final result.

The advantage of async/await is that it offers a clearer and more readable way of handling asynchronous operations without the need for complicated chaining.

Answer 8

When dealing with streams, such as BehaviorSubject, observables are a great choice. However, for a single data call (e.g. http.get()), it's more efficient to make the service call itself asynchronous.

async getSomethingById(id: number): Promise<Something> {
    return await this.http.get<Something>(`api/things/${id}`).toPromise();
}

By doing this, you can simply call the function like this:

async someFunc(): Promise {
    console.log(await getSomethingById(1));
}

Although RxJS is powerful, using it for a basic API call may be excessive. Even if you need to manipulate the retrieved data, you can utilize RxJS operators within the getSomethingById function and return the final result.

The advantage of async/await is that it offers a clearer and more readable way of handling asynchronous operations without the need for complicated chaining.

What are the benefits of pairing Observables with async/await for asynchronous operations?

Answer №1

Sequencing Observables in Your Code

Combining Angular 'async' Pipe with Observables

Considering ES6 async/await and Promises

Answer №2

Blending Promises and Observables

Utilizing Promises in Angular

Regarding Your Example

Answer №3

Answer №4

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