how to use the retrywhen function from the rxjs library in javascript

retryWhen is a function from the RxJS library in JavaScript that allows you to handle errors and retry the observable sequence at your discretion.

Here's an example of how to use retryWhen:

index.tsx
import { interval, throwError } from 'rxjs';
import { mergeMap, retryWhen } from 'rxjs/operators';

const source = interval(1000);

source.pipe(
  mergeMap(val => {
    if (val > 3) {
      return throwError('Error!');
    }
    return of(val);
  }),
  retryWhen(errors => errors.pipe(
    delayWhen(() => timer(1000))
  ))
).subscribe(console.log);
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In this example, we create an observable sequence that emits a value every second (interval(1000)). We then use the mergeMap operator to project each value emitted into either another observable or a value. In this case, we check if the emitted value is greater than 3, and if so, we throw an error using throwError('Error!'). Otherwise, we return the value using of(val).

Next, we use the retryWhen operator to handle any errors that may occur in the sequence. We pass retryWhen a function that takes an observable of errors, which we can then manipulate to retry the observable sequence or not. In this example, we use the delayWhen operator to delay retry attempts by 1 second (delayWhen(() => timer(1000))).

Finally, we subscribe to the sequence and log each emitted value to the console using subscribe(console.log).