Promises vs Observables comparison for functions returning single data (not a data stream)

usingObservables.ts

import { Observable, Subject, ReplaySubject, from, of, range, observable } from 'rxjs';
import { map, flatMap, filter, concatMap, switchMap, delay, tap } from 'rxjs/operators';

function getUserId(userName:string, callback: (id:number) => void){
	let users: { [key: string]: number } = {
		anonymous: -1,
		francois: 1,
		chloe: 2
	};
	setTimeout(() => callback(users[userName] as number), 2000);
}

function getPermissions(id:number, callback: (permissions:string[]) => void){
	let permissions: { [key: number]: string[] } = {
		1: ["r", "w"],
		2: ["r"]
	};
	setTimeout(() => callback(permissions[id]), 2000);
}

function observableGetUserId(userName:string): Observable<number>{
	return new Observable(observer => getUserId(userName, id => observer.next(id)));
}

function observableGetPermissions(id:number): Observable<string[]>{
	return new Observable(observer => getPermissions(id, permissions => observer.next(permissions)));
}

function observablesTest(userName:string){
	observableGetUserId(userName).pipe(
		flatMap(id => {
			console.log("id: " + id);
			if (id === -1){
				return of([]);
			}
			else{
				return observableGetPermissions(id);
			}
		})
	).subscribe(permissions => console.log("permissions: " + permissions.join(",")));
} 

observablesTest("francois");
//observablesTest("anonymous");

usingProxies.ts

function getUserId(userName:string, callback: (id:number) => void){
	let users: { [key: string]: number } = {
		anonymous: -1,
		francois: 1,
		chloe: 2
	};
	setTimeout(() => callback(users[userName] as number), 2000);
}

function getPermissions(id:number, callback: (permissions:string[]) => void){
	let permissions: { [key: number]: string[] } = {
		1: ["r", "w"],
		2: ["r"]
	};
	setTimeout(() => callback(permissions[id]), 2000);
}
//-------------------------------

function promisifiedGetUserId(userName:string): Promise<number>{
	return new Promise(res => getUserId(userName, res));
}

function promisifiedGetPermissions(id:number): Promise<string[]>{
	return new Promise(res => getPermissions(id, res));
}

async function promisesTest(userName:string){
	let id = await promisifiedGetUserId(userName);
	console.log("id: " + id);

	let permissions: string[];
	if (id === -1){
		permissions = [];
	}
	else{
		permissions =  await promisifiedGetPermissions(id);
	}
	
	console.log("permissions: " + permissions.join(","));
} 

//sort of C#'s "async main"
(async () => {
	await promisesTest("francois");
	await promisesTest("anonymous");
})();