Angular Observable, Promiseの相互変換

ObservableもPromiseも、似たようなもんだと思ってます。

import { from as fromPromise } from 'rxjs';

const foo = this.http.get('http://localhost:3000/')
console.log(foo) // Observable
foo.subscribe(res => console.log(1, res))

const bar = foo.toPromise()
console.log(bar) // Promise
bar.then(res => console.log(2, res))

const baz = fromPromise(bar)
console.log(baz) // Observable
baz.subscribe(res => console.log(3, res))