What is the proper way to terminate a Promise.all() in Angular 2?

Question

What is the proper way to terminate a Promise.all() in Angular 2?

My current sign-up process involves a Promise.all() being made on every "next" click, resulting in multiple http requests. However, when users quickly click through the process, these requests start to pile up and cause issues with my app.

Is there a way for me to cancel a Promise.all() if a new one is triggered before the previous one has completed? I need a solution to prevent these build-ups of requests causing problems with the functionality of my app.

javascript angular typescript promise

Answer 1

Answer №1

While promises can be waited on to finish, there is no built-in cancellation feature.

An approach could be to prevent the user from progressing using a disabled next button until all promises are resolved.

<button [disabled]="completed">Next</button>

Answer 2

While promises can be waited on to finish, there is no built-in cancellation feature.

An approach could be to prevent the user from progressing using a disabled next button until all promises are resolved.

<button [disabled]="completed">Next</button>

Answer 3

Answer №2

To enhance the functionality, I would implement observables along with switchMap and debounceTime. Here's a sample approach:

export class MyComponent implements OnInit {
  actions: Observable<any[]>;
  private signals = new Subject<string>();
  constructor() {}

  submit(signal: string): void {
    this.signals.next(signal);
  }

  ngOnInit(): void {
    this.actions = this.signals
      .debounceTime(300)        
      .distinctUntilChanged()
      .switchMap(signal => {
         // Perform HTTP calls based on the signal e.g
         // return this.service.getAction(signal)
      })
      .catch(error => {
        // Handle any errors
      });
  }
}

This logic is inspired by the tutorial at https://angular.io/docs/ts/latest/tutorial/toh-pt6.html#!#-_observable-s

An advantage of using switchMap is that it can cancel ongoing HTTP requests if another signal is received. However, it's important to note that this feature is only beneficial if your server is capable of handling cancelled requests effectively.

Answer 4

To enhance the functionality, I would implement observables along with switchMap and debounceTime. Here's a sample approach:

export class MyComponent implements OnInit {
  actions: Observable<any[]>;
  private signals = new Subject<string>();
  constructor() {}

  submit(signal: string): void {
    this.signals.next(signal);
  }

  ngOnInit(): void {
    this.actions = this.signals
      .debounceTime(300)        
      .distinctUntilChanged()
      .switchMap(signal => {
         // Perform HTTP calls based on the signal e.g
         // return this.service.getAction(signal)
      })
      .catch(error => {
        // Handle any errors
      });
  }
}

This logic is inspired by the tutorial at https://angular.io/docs/ts/latest/tutorial/toh-pt6.html#!#-_observable-s

An advantage of using switchMap is that it can cancel ongoing HTTP requests if another signal is received. However, it's important to note that this feature is only beneficial if your server is capable of handling cancelled requests effectively.

Answer 5

Answer №3

When it comes to "canceling a Promise.all()", the idea is to ensure that the promise returned by a Promise.all() does not continue on its success path.

While Promises themselves are not cancelable, there are pattern-based solutions that can achieve a similar effect.

The basic concept behind this approach is fairly straightforward. Essentially, within each batch of promises, you can include a special promise that:

will be resolved if the current batch is successful
will be rejected once the next batch is initiated

This sets up a sort of competition between different outcomes.

The challenge lies in seamlessly integrating this "super-aggregation" into the final results.

Here is one possible implementation - although it may not be the most concise, there could be more efficient ways to accomplish this task.

function BatchCanceller() {
    // Return a function that takes an array of promises and returns an aggregated promise.
    // Use this returned function similarly to how you would use $q.all().
    var dfrd;
    return function(promises) {
        if(dfrd) {
            dfrd.reject(new Error('cancelled')); // reject previous batch
        }
        dfrd = $q.defer();
        
        // Prepare for all promises to resolve `dfrd` if successful.
        $q.all(promises).then(dfrd.resolve);
        
        // Include `dfrd` in a super-aggregation of promises.
        return $q.all(promises.concat(dfrd.promise)).then(function(results) {
            // If the aggregated promises succeed, remove the last result (from `dfrd`)
            return results.splice(0, results.length-1);
        });
    };
}

var batchCanceller = new BatchCanceller();

var promises = [/* whatever */];
batchCanceller(promises).then(function(results) {
    console.log(results);
}).catch(function(error) {
    console.log(error); // will display "cancelled" if another batchCanceller(promises) is called before the previous one resolves
});

In practical applications, it might be more suitable to implement BatchCanceller() as an Angular factory.

Answer 6

When it comes to "canceling a Promise.all()", the idea is to ensure that the promise returned by a Promise.all() does not continue on its success path.

While Promises themselves are not cancelable, there are pattern-based solutions that can achieve a similar effect.

The basic concept behind this approach is fairly straightforward. Essentially, within each batch of promises, you can include a special promise that:

will be resolved if the current batch is successful
will be rejected once the next batch is initiated

This sets up a sort of competition between different outcomes.

The challenge lies in seamlessly integrating this "super-aggregation" into the final results.

Here is one possible implementation - although it may not be the most concise, there could be more efficient ways to accomplish this task.

function BatchCanceller() {
    // Return a function that takes an array of promises and returns an aggregated promise.
    // Use this returned function similarly to how you would use $q.all().
    var dfrd;
    return function(promises) {
        if(dfrd) {
            dfrd.reject(new Error('cancelled')); // reject previous batch
        }
        dfrd = $q.defer();
        
        // Prepare for all promises to resolve `dfrd` if successful.
        $q.all(promises).then(dfrd.resolve);
        
        // Include `dfrd` in a super-aggregation of promises.
        return $q.all(promises.concat(dfrd.promise)).then(function(results) {
            // If the aggregated promises succeed, remove the last result (from `dfrd`)
            return results.splice(0, results.length-1);
        });
    };
}

var batchCanceller = new BatchCanceller();

var promises = [/* whatever */];
batchCanceller(promises).then(function(results) {
    console.log(results);
}).catch(function(error) {
    console.log(error); // will display "cancelled" if another batchCanceller(promises) is called before the previous one resolves
});

In practical applications, it might be more suitable to implement BatchCanceller() as an Angular factory.

What is the proper way to terminate a Promise.all() in Angular 2?

Answer №1

Answer №2

Answer №3

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