concat

concat multiple observables, before show next concatenated observable, current observable should be finished

Example: normal use

import { concat, interval } from 'rxjs';
import { take } from 'rxjs/operators';
 
const t1$ = interval(1000).pipe(take(3));
const t2$ = interval(2000).pipe(take(4));
const t3$ = interval(500).pipe(take(4));
 
const concat$ = concat(t1$, t2$, t3$);

Example: ⚠️⚠️⚠️wrong use⚠️⚠️⚠️

import { concat, interval } from 'rxjs';
import { take } from 'rxjs/operators';
 
const t1$ = interval(1000); // this observable isn't finished
const t2$ = interval(2000).pipe(take(4));
const t3$ = interval(500).pipe(take(4));
 
const concat$ = concat(t1$, t2$, t3$);

Official Doc: rxjs.concat