Hot or Cold: What\'s the Difference in RxJS Observables?

Hot and Cold Observables: Unveiling the Differences

Cold Versus Hot: A Refresher

Observables in RxJS can be categorized as either hot or cold. Cold observables emit values only when subscribed to, while hot observables emit values regardless of subscription status.

Confusion Resolved

• Are all RxJS observables cold by default?

  Yes, except for subjects.

• Can cold observables be converted to hot?

  Yes, using operators like publish(), share(), and the multicast operators (publishValue, shareValue, etc.).

• Behavior of withLatestFrom with Cold Observables

  Let cold$ be a subscribed cold observable. withLatestFrom(cold$, ...) creates a new observable that will emit values from cold$ immediately upon subscription, regardless of when cold$ was initially subscribed to.

FromEvent() and Shared Click Events

RxJS.fromEvent() creates cold observables by default. However, the CodePen example you mentioned shows different values for different subscriptions because it uses RxJS version 4, which employs a different behavior for fromEvent().

Detailed Flow of Cold and Hot Observables

Cold Observable:

1. Subscription triggers chain of subscriptions upstream.
2. Last subscription executes a function that handles a source and emits data to its observer.
3. Data flows downstream to the sink observer.

Hot Observable:

1. Multicast operator creates a subject and returns a connectable observable.
2. Subscriptions to the operator subscribe to the subject.
3. When connect is called, the subject subscribes to the upstream observable, and data flows downstream.

Conclusion

Understanding the flow of data through observables and the implementation of operators is crucial for navigating the complexities of hot and cold observables. The key considerations are the timing of data emission relative to subscriptions and the potential for lost or duplicated data due to multiple subscriptions.

The above is the detailed content of Hot or Cold: What\'s the Difference in RxJS Observables?. For more information, please follow other related articles on the PHP Chinese website!