TypeScript

RxJs---observables.ts

/*
    Observables are a representation of any set of values
    over any amount of time.
*/

import {map, tap} from '@rxjs/operators'

getOldBookById(id: number): Observable<OldBook>{
	return this.http.get<Book>(`/api/books/${id}`)
	.pipe(
	map(b => <OldBook>{
		bookTitle: b.title,
		year: b.publicationYear
	}),
	tap(classicBook => console.log(classicBook))
	);
}