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

The exhaustMap() function is used in reactive programming, specifically with the rxjs library in JavaScript. It is commonly used when you have a stream of events, and you want to map each event to an observable, and then flatten the result into a single observable. During this process, if there are multiple events, only the first observable is kept, and the others are ignored until the first observable completes.

Here's an example of how to use exhaustMap() in JavaScript:

index.tsx
import { fromEvent } from 'rxjs';
import { exhaustMap } from 'rxjs/operators';

const button = document.querySelector('button');
fromEvent(button, 'click')
  .pipe(
    exhaustMap(() => {
      // replace this with any observable that you want to map the click event to
      return fetchData();
    })
  )
  .subscribe((result) => console.log(result));
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In the example above, we're using fromEvent() to create a stream of click events on a button. These events will be passed through the exhaustMap() operator, which will map each click event to an observable returned by the fetchData() function. In this example, only the first click event will result in a call to fetchData(), since exhaustMap() will ignore any subsequent events until the first one completes.

Note that in order to use exhaustMap(), you need to import it from the rxjs/operators package, and then use it in your observable chain with the pipe() function.