Events

Strategies report events to the instrumentation of the execution. Every event has a type. attempt is 1-based.

type	Fields	Reported by
retry.scheduled	attempt, delayMs, error or value	Retry
retry.exhausted	attempts, error or value	Retry
retry.declined	attempt, error or value, reason: 'budget', 'idempotency' or 'delay'	Retry
timeout	attempt, timeoutMs	Timeout
circuit.state_changed	breaker, from, to	Circuit breaker
circuit.rejected	breaker, state, retryAfterMs	Circuit breaker
bulkhead.rejected	bulkhead, running, queued	Bulkhead
fallback.used	error	Fallback
fallback.stale	key, ageMs	Stale fallback
rate_limit.rejected	key, retryAfterMs	Rate limit
lock.rejected	key	Lock
dedupe.joined	key	Dedupe
cache.hit	key	Cache
cache.miss	key	Cache
cache.stale	key, error	Cache
cache.failed	key, error	Cache
custom	name, attributes?	Custom strategies

The union of these shapes is the TenaceEvent type. A switch on event.type narrows it:

import { listener, type TenaceEvent } from '@julr/tenace'

function describeEvent(event: TenaceEvent): string {
  switch (event.type) {
    case 'retry.scheduled':
      return `retry ${event.attempt} in ${event.delayMs}ms`
    case 'circuit.state_changed':
      return `${event.breaker}: ${event.from} -> ${event.to}`
    default:
      return event.type
  }
}

const instrumentation = listener(event => logger.info(describeEvent(event)))