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

The scan operator, imported from the rxjs library, is used in reactive programming to accumulate values emitted by an observable over time. It is similar to the reduce method of arrays, but instead of returning a final value, it emits an accumulated value for each incoming item. Here's an example usage of scan:

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

const numbers = [1, 2, 3, 4, 5];
const observable$ = from(numbers);

const sum$ = observable$.pipe(
  scan((acc, curr) => acc + curr, 0)
);

sum$.subscribe(sum => console.log(sum));
// output: 1, 3, 6, 10, 15
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In this example, we create an observable called observable$ that emits the numbers from an array using the from method. We then use the scan operator to accumulate the values emitted by the observable.

The first argument to scan is a callback function that takes two parameters: the accumulated value (acc), and the current value (curr). In this case, we are simply adding the current value to the accumulated value.

The second argument to scan is the initial value of the accumulated value (0 in this example). The operator emits the accumulated value for each incoming item, which is then logged to the console by the subscribe method.

This is just a simple example, but scan can be used in more complex scenarios to accumulate state over time in a reactive programming environment.