More Rxjs Transformation Operators — Scan and Window

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Rxjs is a library for doing reactive programming. Creation operators are useful for generating data from various data sources to be subscribed to by Observers.

In this article, we’ll look at how to use transformation operators scan , switchMap , switchMapTo and window .

scan

The scan operator applies an accumulator function over the source Observation by combining the emitted values. Then it returns each intermediate result, with an optional seed value.

It takes up to 2 arguments. The first is the accumulator function, which is the function that combines the value that was accumulated so far with the new emitted value.

The second is an optional argument, which is the seed , or the initial accumulation value.

For example, we can use it as follows:

import { of } from "rxjs";
import { scan } from "rxjs/operators";
const of$ = of(1, 2, 3);
const seed = 0;
const count = of$.pipe(scan((acc, val) => acc + val, seed));
count.subscribe(x => console.log(x));

The code above starts with an of Observable and a seed initial value of 0. Then we pipe the values from the of$ Observable to the scan operator, which has the accumulation function, which adds the…