Logging

composurejs logs structured entries: one object per line, with a msg and fields. Everything logged while answering an Interaction carries its fields, whether core logged it, your handler did, or a REST call or Background Work did:

Field
interactionId, interactionType	Which Interaction.
command	The Command's name, for Commands and autocomplete.
handler	The handler's id, for clicks and modal submits (never the values it carries).
guildId, userId	Where and who.
event	The type, for Webhook Events.

In handlers

c.log is the logger with those fields bound. Middleware, handlers and Event Handlers all have it:

export const grant = command({
  name: "grant",
  description: "Grant the role",
  handler: (c) => {
    c.log.info({ msg: "Role granted", roleId: "123" })
    return "Done."
  },
})

Pass errors as fields. They are written with their cause chain, and a DiscordApiError keeps its status, code and per-field errors. Never log the Interaction token or a URL that contains it.

Levels and formats

The default is info and above. debug adds REST responses, retries, Auto Defers, Fallbacks and User Errors. The App takes options for the built-in logger:

const app = new App({ logger: { level: "debug", format: "json" } })

• object (the default on Workers) makes one console call with an object, which Workers Logs indexes by field.
• pretty (the default elsewhere) writes LEVEL msg key=value, then error stacks. It's made for reading in a terminal.
• json writes one JSON line with time and level, for log pipelines on Node and Bun.

createLogger(options) builds the same logger for use outside the App. fields adds fields to every entry, for example { service: "bot" }.

Your own logger

Pass any object with debug, info, warn and error. Each method receives one entry object. pino's loggers work as they are, and their child is used to bind fields:

const app = new App({ logger: pino() })

A logger without child is wrapped, and the bound fields are merged into each entry.

In tests

recordLogs() keeps every entry with its level and bound fields:

import { expect, test } from "vitest"
import { answer, chatInput, recordLogs } from "composurejs/testing"

test("pinging logs nothing above info", async () => {
  const logs = recordLogs()
  await answer(new App({ logger: logs.logger }).command(ping), chatInput("ping"))
  expect(logs.entries.filter((e) => e.level === "warn" || e.level === "error")).toEqual([])
})