try

import {Obsrevable} from 'rxjs';

import {Observable} from 'rxjs';

in addition, there are official Angular tutorials that you can refer to

ide/observables" rel=" nofollow noreferrer "> Angular official tutorial

Let's ask and answer your own question. The code similar to Rx.Observable above is used before 5.5.It is now more than 6, so destructive updates
should be quoted as follows: import {delay} from 'rxjs/operators'; , using
of (xxxx) .pipe (delay (2000)); , indicating that you have to wait 2 seconds before the observable object is returned