Angular2 Observable and Promise

Question

I started using Angular2 Observable, but I can\'t find something similar to .then that I used with Promises.

This is what I want

Answer 1

When you call subscribe(...) a Subscription is returned which doesn't have a toPromise(). If you move the code from subscribe to map you can use toPromise() instead of subscribe

return this._httpClient.post('LoginAction', credentials)
  .map(res => res.json())
  .map(user => {
    return new User(user);
  }).toPromise();

and the caller will get a Promise where he can get the value using

public login() {
    this._user = AuthService.getInstance().login(this._loginInfo)
    .then(result => {
      doSomething();
    });
}

but you get the same result if you omit `.toPromise() and the caller uses it like

public login() {
    this._user = AuthService.getInstance().login(this._loginInfo)
    .subscribe(result => {
      doSomething();
    });
}

where the only difference is subscribe() instead of then() and if the user of the library prefers the reactive style he will prefer using subscribe() like he is used to.

Answer 2

From Angular2 documentation

We are advise to add this in rxjs-extension.ts

```
// Observable class extensions 
   import 'rxjs/add/observable/of'; 
   import 'rxjs/add/observable/throw';

// Observable operators 
   import 'rxjs/add/operator/catch'; 
   import 'rxjs/add/operator/debounceTime'; 
   import 'rxjs/add/operator/distinctUntilChanged'; 
   import 'rxjs/add/operator/do'; 
   import 'rxjs/add/operator/filter'; 
   import 'rxjs/add/operator/map'; 
   import 'rxjs/add/operator/switchMap'; 
```

And import it at app.module.ts (Root Module) import './rxjs-extensions';

This will help us to prevent further error.

Answer 3

You need to import the Rx toPromise operator like

import 'rxjs/add/operator/toPromise';

Cheers!