Observables

One can subscribe to observables (don't forget to unsubscribe in ngOnDestroy) and get their values one by one, all at once, combined, reduced, transformed etc.

In angular templates use the async pipe to create ad hoc subscriptions: {{name$ | async}}.

See examples.

Observables vs subjects

Observables:

• cold: executed on (every) subscribe
• we can't change its value "from the outside" (uni-directional, unicast)
• ex.: from(aPromise), from(rxAjax)...

Subjects:

• hot: "runs" even if there are no subscribers
• same data is shared among subscribers
• new values can be "added" in time (bi-directional, multicast)
• use BehaviorSubject if you need access to the last emitted value
• use ReplaySubject if you need access to all the values (replayed)

Creating observables using shorthands

• of: of(1, 2, 3) = array-like list
• from: array-like, iterable (yields), collection (maps), promise, observable-like
  • from([1, 2, 3])
  • from('abcdefg) (a → b → c ... g)
  • from(fetch('api/data'))
• interval: interval(1000)
• event: fromEvent(document, 'click')
• ajax: ajax('/api/data') (import ajax from rxjs/ajax first)
• others: create, empty, generate, range, throw, timer