Structured logging with child contexts. JSON in production, pretty in dev.

Installation

npm install @prsm/log

Usage

import log from '@prsm/log'

log.info('server started', { port: 8080 })
log.warn('slow query', { ms: 1200 })
log.error(new Error('connection refused'))

Pretty output (dev):

[14:32:01] INFO  server started
    port: 8080
[14:32:01] WARN  slow query
    ms: 1200
[14:32:01] ERROR connection refused
    err: connection refused

JSON output (production):

{"level":"info","msg":"server started","port":8080,"ts":1710782521000}

Child Contexts

Create loggers that carry context through a request, job, or connection.

const conn = log.child({ connId: 'abc-123' })
conn.info('command received', { cmd: 'submit' })
// [14:32:01] INFO  command received
//     connId: abc-123
//     cmd: submit

const db = conn.child({ db: 'postgres' })
db.info('query', { ms: 12 })
// [14:32:01] INFO  query
//     connId: c1
//     db: postgres
//     ms: 12

Context accumulates. Every log from a child includes all parent context.

Configuration

log.configure({
  level: 'debug',  // debug | info | warn | error | none
  pretty: false,   // true for human-readable, false for JSON
})

Defaults: level info, pretty when NODE_ENV !== 'production'.

Tracing Across Subsystems

Pass context through queue jobs, realtime commands, workflows.

server.exposeCommand('submit', async (ctx) => {
  const l = log.child({ connId: ctx.connection.id })
  l.info('received')
  await queue.push({ ...ctx.payload, _trace: l.context })
})

queue.process(async (payload, task) => {
  const l = log.child({ taskId: task.uuid, ...payload._trace })
  l.info('processing')
  // every log line carries connId + taskId
})

License

MIT