concatAll.ts

const pokemonId$ = of(1, 5, 6);

function getPokemonName(id: number) {
  return ajax.getJSON(`https://pokeapi.co/api/v2/pokemon/${id}`).pipe(
    map(({ name }) => name),
    delay(2000)
  );
}

// concatAll subscribes to each inner Observable only after the previous one has completed: it will wait until each request is done, before making a new one
pokemonId$
  .pipe(
    map(id => getPokemonName(id)),
    concatAll()
  )
  .subscribe(console.log);
// Output: (2s) bulbasaur, (2s) charmeleon, (2s) charizard