RxJS mergeMap

 flatMap is deprecated and replaced by mergeMap

import { of, mergeMap, interval, map, take } from 'rxjs';

const letters = of('a', 'b', 'c');

const result = letters.pipe(

mergeMap((x) =>

interval(1000).pipe(

take(4),

map((i) => x + i)

)

)

);

result.subscribe((x) => console.log(new Date().toISOString()x));

// Results in the following:

// a0

// b0

// c0

// a1

// b1

// c1