Reactors

Reactors are documented in the shared Chronicle docs with synchronized examples for C#, Kotlin, Java, Elixir, and TypeScript.

• Getting started with reactors
• Reactor event processing
• Returning side effects
• Replay
• Reactors overview

Use the TypeScript get started page for package installation and connection setup.

TypeScript client notes

A reactor handler method can now return a side effect instead of only observing: a single event, an array of events, a single EventForEventSourceId (to target an event source other than the one that triggered the reactor), an array of those, or a mix. Whatever is returned is appended in one atomic appendMany call once the handler completes — a bare event uses the triggering event’s own event source id, stream, and subject; an EventForEventSourceId entry keeps its own target. If the side-effect append fails, the reactor’s partition is marked Failed, the same as if the handler itself had thrown.

A @reactor/@reducer-decorated class instance can also optionally implement ICanBeNotifiedWhenReplay (beginReplay/endReplay) and/or ICanBeNotifiedWhenPartitionReplayed (beginReplayPartition/endReplayPartition, both given the partition) to be notified when a replay begins and ends, at the full-observer or per-partition granularity.