map

map Operator allows you change emit results by project function

Example: map operator change emit value

import { interval } from 'rxjs';
import { map, take } from 'rxjs/operators';

const source$ = interval(1000).pipe(take(20));

const result$ = source$.pipe(map(value => value * 10));

Example: Map operator, projects new observable

you also can emit new observables as value, see this example:

import { interval } from 'rxjs';
import { map, take } from 'rxjs/operators';

const source$ = interval(2000).pipe(take(3));
const projection$ = interval(1000).pipe(take(5))

const result$ = source$.pipe(map(value => projection$));

Official Doc: rxjs.map