Do you understand observables
An Observable Workshop
Do you understand observables? I didn’t, and probably still don’t
What is the difference between an Observable and a function? Observables can “return” multiple values over time, something which functions cannot.
What is an Observer? An Observer is a consumer of values delivered by an Observable. Observers are simply a set of callbacks, one for each type of notification delivered by the Observable: next, error, and complete. The following is an example of a typical Observer object:
var observer = {
next: x => console.log(`Observer got a next value: ${x}`),
error: err => console.error(`Observer got an error: ${err}`),
complete: () => console.log(`Observer is complete`)
};
To use the Observer, provide it to the subscribe of an Observable:
observable.subscribe(observer);
Observers are just objects with three callbacks, one for each type of notification that an Observable may deliver.
Observers in RxJS may also be partial. If you don’t provide one of the callbacks, the execution of the Observable will still happen normally, except some types of notifications will be ignored, because they don’t have a corresponding callback in the Observer.
The example below is an Observer without the complete callback:
var observer = {
next: x => console.log(`Observer got a next value: ${x}`),
error: err => console.error(`Observer got an error: ${err}`)
};
When subscribing to an Observable, you may also just provide the callbacks as arguments, without being attached to an Observer object, for instance like this:
observable.subscribe(x => console.log(`Observer got a next value:${x}`));
Internally in observable.subscribe, it will create an Observer object using the first callback argument as the next handler. All three types of callbacks may be provided as arguments:
observable.subscribe(
x => console.log(`Observer got a next value: ${x}`),
err => console.error(`Observer got an error: ${err}`),
() => console.log(`Observer got a complete notification')
);
Resources: