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

The concatWith function from the rxjs library in JavaScript is used to concatenate multiple observable sequences together in the order they are passed as parameters. It is one of the many operators available in RxJS.

Here's an example of how to use it:

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

const source1$ = of(1, 2, 3);
const source2$ = of(4, 5, 6);

source1$.pipe(concatWith(source2$)).subscribe(result => console.log(result));

// Output: 1 2 3 4 5 6
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In this example, we have created two observables - source1$ and source2$, both using the of function to emit values. We then use the pipe method to chain the concatWith operator onto source1$. This takes source2$ as its argument and when subscribed to, will emit all the values from source1$ followed by all the values from source2$.

Note that the concatWith operator does not start emitting values until source1$ completes. If you want to start emitting values from source2$ immediately without waiting for source1$ to complete, you can use the concat operator instead.