Defining Listeners

Define listeners with defineListener(...) from @holo-js/events.

Single-event listener

import { defineListener } from '@holo-js/events'
import UserRegistered from '../events/user/registered'

export default defineListener({
  listensTo: [UserRegistered],
  async handle(event) {
    await analytics.track('user.registered', {
      userId: event.payload.userId,
    })
  },
})

handle(event) receives an envelope with:

• event.name
• event.payload
• event.occurredAt

Listener identity

Listeners can have an explicit name:

export default defineListener({
  name: 'users.send-welcome-email',
  listensTo: [UserRegistered],
  async handle(event) {
    await mailer.sendWelcome(event.payload.email)
  },
})

If name is omitted for discovered app listeners, Holo-JS derives an id from the file path under server/listeners.

Queued listener options

Set queue: true for queued execution:

export default defineListener({
  listensTo: [UserRegistered],
  queue: true,
  connection: 'redis',
  queueName: 'emails',
  delay: 30,
  async handle(event) {
    await mailer.sendWelcome(event.payload.email)
  },
})

Queued metadata fields:

• connection
• queueName
• delay

These require queue: true.

Listener-level afterCommit

Listener-level deferral:

export default defineListener({
  listensTo: [UserRegistered],
  queue: true,
  afterCommit: true,
  async handle(event) {
    await projections.syncUser(event.payload.userId)
  },
})

This defers only this listener when a transaction is active.

Continue

• Multi-Event Listeners
• Queued Listeners