Why is there a toPromise method in angular 4?

Question

JavaScript

Hello.
I have a method
getAllUsers(){
return this.http.get('/api/users')
.map(res => res.json());
}
The documentation says that you need to use the Promise method. Why is it needed?
getAllUsers(): Promise {
return this.http.get('/api/users')
.toPromise()
.then(response => response.json().data as User[])
.catch(this.handleError);
}
Thank you.

Answer 1

Because observable is there by default