Observable concatMap

observable2.js

const { from } = require('rxjs');
const { concatMap } = require('rxjs/operators');

const getUserId = () => {
  return from(['1337']);
};

const getUserById = id => {
  return from([
    {
      id: '1337',
      name: 'mika'
    }
  ]);
};

const apiRequest = getUserId().pipe(
  concatMap(userid => {
    console.log(userid);
    return getUserById(userid);
  })
);

apiRequest.subscribe(
  data => console.log(data),
  error => console.log(error),
  () => console.log('complete')
);