[What's New in RxJS 7] Better types in groups created by groupBy #blog #rxjs

rxjs-7_groupBy-key.ts

import { of } from "rxjs";
import { groupBy, map, mergeMap } from "rxjs/operators";

// Observable<string, number>
of(0, "A", 1, "B", 2, "C", 3, "D", 4, "E", 5, "F", 6, "G", 7, "H", 8, "I", 9, "...")
  .pipe(
    groupBy((x): x is number => typeof x === "number"),
    mergeMap(group$ => (group$.key === true ? group$.pipe(map(String)) : group$))
  )
  .subscribe();
// Observable<string> (in RxJS 6 → Observable<string | number>)