Observables and Promises.

Observables are just like promises.

promise.then(
    successFn,
    errorFn,
);

observable.subscribe(
    nextFn,
    errorFn,
    completeFn,
);

---

Observables. Structure.

var observable = Rx.Observable.create(observer => {
    observer.next(VALUE);
    ...
    observer.complete();
});
observable.subscribe({
    next: value => console.log(value);
    error: err => console.error('something wrong occurred: ' + err),
    complete: () => console.log('done'),
})

---

Create Observables.

• create - create an observable with given subscription function;
• fromEvent - turn event into observable;

---

RxJs. Operators.

Operators take your observable and return a new observable.

Familiar:

• map - map one Observable in another Observable (synchronous way);
• filter - pass only data that has correct conditions;
• debounceTime - like debounce;
• distinctUntilChanged - pass only if data is changed;
• throttleTime - like throttle;
• reduce - like reduce;
• scan - similar to reduce, but it can provide intermediate values;
• pluck - extract properties from the object;
• mergeMap - can combine data from two Observables, one observable in another (asynchronous way);
• switchMap - allow to trigger some values emission whenever another observable emits a value;
• from - turn an array, promise, or iterable into an observable;
• of - emit variable amount of values in a sequence;
• concat - subscribe to observables in order as previous completes, emit values;

Not used yet:

• takeUntil - two observables, emit first until second provided observable values;
• take - emit provided number of values before completing;
• combineLatest - when any observable emits a value, emit the latest value from each;
• tap - operator for perform actions or side-effects, such as logging, does not transform values (ex. do);
• merge - turn multiple observables into a single observable;
• forkJoin - when all observables complete, emit the last emitted value from each;
• pairwise - emit the previous and current values as an array;
• combineLatest - when any observable emits a value, emit the latest value from each.
• concatMap - map values to inner observable, subscribe and emit in order;
• race - the observable to emit first is used;
• ignoreElements - ignore everything but complete and error;

---

Redux-observable.

1. Observables in Redux-observable === Epics;
2. Observer in Redux-observable === store.dispatch;
3. Epic main principle: Action IN => Action OUT;
4. Final scheme:
epic(action*, store).subscribe(store.dispatch)