ReactionResolver

@rotorsoft/act-root

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@rotorsoft/act-root / act/src / ReactionResolver

Type Alias: ReactionResolver<TEvents, TKey, TLane>

ReactionResolver<TEvents, TKey, TLane> = Resolved<TLane> | ((event) => Resolved<TLane> | undefined)

Defined in: libs/act/src/types/reaction.ts:116

Resolver for determining which stream a reaction should target.

Resolvers enable dynamic reaction routing based on event content. They can be:

• Static: Always route to the same target stream
• Dynamic: Determine target based on event data at runtime

Resolvers can also specify source streams for optimization, allowing the drain process to efficiently fetch only relevant events. An optional priority biases the lagging-frontier claim() ordering — see Resolved.priority.

Type Parameters

TEvents

TEvents extends Schemas

Event schemas

TKey

TKey extends keyof TEvents

Event name

TLane

TLane extends string = string

Param

event

The committed event (for dynamic resolvers)

Returns

Target stream configuration or undefined to skip

Examples

Static target

.on("UserCreated")
  .do(sendWelcomeEmail)
  .to("email-queue") // Static target

Dynamic target per user

.on("UserLoggedIn")
  .do(incrementLoginCount)
  .to((event) => ({
    target: `stats-${event.stream}` // Dynamic per user
  }))

With source optimization

.on("UserUpdated")
  .do(updateReadModel)
  .to(({ stream }) => ({
    source: stream,           // Only fetch from this user's stream
    target: `cache-${stream}` // Update corresponding cache
  }))

With priority (saturated worker scheduling)

.on("OrderConfirmed")
  .do(sendCriticalNotification)
  .to({ target: "notifications-out", priority: 10 })

See

• Reaction for complete reaction configuration
• Resolved for the resolved-target shape