Use case of Observable .do() operator (rxjs)

Question

 Context :

I'm building an angular 2 app (with a Firebase API). I'm using the AngularFire module. I was wondering how I can mix the canActivate method with the AngularFire auth Observable, and I found this post. The answer is to make the canActivate method returns an Observable<boolean> :

canActivate(): Observable<boolean> {   return this.auth     .take(1)     .map((authState: FirebaseAuthState) => !!authState)     .do(authenticated => {       if (!authenticated) this.router.navigate(['/login']);     }); } 

It's the first time I see the Observable do operator, and I can't understand what it really does ? The official doc didnt help me, and I didn't found decent examples.

Question:

Can someone bring here some examples of .do() usage ? And difference with .subscribe() ?

Answer 1

Update

Now it's pipe( tap(...), ) instead of do()

Original

.do() is to execute code for each event. A difference to .map() is, that the return value of .do() is ignored and doesn't change what value the subscriber receives.

Answer 2

Now it's pipe( tap(...), ) instead of do()

const source = of(1, 2, 3, 4); source.pipe(   tap(val => console.log('I am tap: ',val)),   filter(val =>  val > 2),   map(val => val + 1)).subscribe((val) => {   console.log('I am subscriber value after filtering: ', val); }); 

Output:

I am tap:  1 I am tap:  2 I am tap:  3 I am subscriber value after filtering:  4 I am tap:  4 I am subscriber value after filtering:  5 

*Tap operator doesn't modify anything, you can say that it is just to view the stream.