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

The windowWhen function is an operator in the ReactiveX library for JavaScript (RxJS) and it creates a new Observable window whenever the specified closingSelector function emits. This operator is used to split up an Observable sequence into multiple Observable windows, which emit a group of values based on a given condition.

Here's an example of how to use the windowWhen function in RxJS:

index.tsx
import { fromEvent } from 'rxjs';
import { windowWhen, mergeAll } from 'rxjs/operators';

// Create an Observable stream from a button click event
const button = document.querySelector('button');
const clickStream = fromEvent(button, 'click');

// Split up the click stream into windows every 5 seconds
const windowStream = clickStream.pipe(windowWhen(() =>
    // Create a new Observable that emits after 5 seconds
    interval(5000)
));
 
// Merge all the window streams into a single stream
const mergeStream = windowStream.pipe(mergeAll());
 
// Subscribe to the merged stream
mergeStream.subscribe(x => console.log(x));
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In the code example above, we first create an Observable stream clickStream from a button click event. We then use the windowWhen operator to split up the click stream into windows every 5 seconds.

The windowWhen operator takes in a closingSelector function, which returns an Observable that represents the closing criterion for the windowed Observable. In our case, we create a new Observable that emits after 5 seconds using the interval function.

Next, we use the mergeAll operator to flatten all the window streams into a single stream. Finally, we subscribe to the merged stream and log the emitted values.

This is just a basic example and there are many more use cases for the windowWhen operator.