Q: Angular2: 'switchMap' does not exist on type 'Observable<Params>'

You need to import the switchMap operator:

import 'rxjs/add/operator/switchMap';

update for rxjs >=5.5.0:

for [email protected] or higher it's recommended to use the pipe operator instead of augmentation:

import { switchMap } from 'rxjs/operators';

\\...

this.route.params.pipe(switchMap((params: Params) => /*... */))
  .subscribe(/*... */);
\\...

(this avoids side effects and enable better bundle size optimization)

import { Observable, of } from 'rxjs';

import { switchMap } from 'rxjs/operators';   


this.user = this.afAuth.authState.pipe(switchMap(user => {

        if (user) {

          return this.afs.doc<User>(`users/${user.uid}`).valueChanges()

        } else {

          return of(null)

        }

      }));

    } 

This issue has been fixed, check below:

    this.route.params.forEach((params: Params) => {
      if (params['id'] !== undefined) {
        let id = +params['id'];
        this.heroService.getHero(id)
            .then(hero => this.hero = hero);
      } 
    });