RxJS
RxJS is a JavaScript library for composing observable sequences of events into a reactive model.
Terminology
| Term | Meaning |
|---|---|
| Observable | An object that emits events |
| Observer | A collection call-backs invoked by an Observable when an event is emitted |
| Operator | A pure function that transforms data emitted by an observable |
| Pipe | |
| Scheduler | |
| Subject | |
| Subscription | The connection between an observable and observer |
Observables
Observables are sometimes referred to as "observable sequences" or "streams" and emit events either synchronously (immediately, when the event occurs) or asynchronously (some time after the event occurs).
Observers
Observers "observe" events emitted by observables.
| Function | Purpose |
|---|---|
next() | Provide a callback to process an event emitted by an observable |
error() | Provide a callback to process an error emitted by an observable |
complete() | Provide a callback to process the end of the observable stream |
Subscriptions
Subscriptions connect observables to observers and are created by calling the subscribe method on an observable and passing it an observer. Events are only emitted to an observer that has subscribed to an observable.
Subscriptions are stopped when:
- The
complete()method is called on the observer - A completing operator is used (for example,
of,from, ortake) - An uncaught error occurs
- When
unsubscribe()is called on a subscription
Broader Topics Related to RxJS
JavaScript
The language of the web until WASM takes over
Reactive Programming
A declarative programming paradigm for extracting and transforming data from streams