@molecule/app-logger

Frontend logging interface for molecule.dev.

Provides a unified logging API that can be backed by different implementations (console, loglevel, remote logging, etc.). Works with ZERO wiring: on first use a console-backed provider is auto-bonded (level 'debug' in development, 'info' otherwise) — call setProvider only to swap in a custom provider.

Auto-generated, AI-first package reference for the molecule.dev ecosystem. It is written to be read by coding agents as much as by people, and is generated from this package's source — edit src/index.ts JSDoc, not this file.

Quick Start

import { createLogger, error, warn } from '@molecule/app-logger'

warn('cache miss', { key }) // root logger — no setup needed
error(err) // error() accepts an Error directly

const log = createLogger('sync') // named/namespaced logger
log.debug('starting', { count })

Type

core

Installation

npm install @molecule/app-logger @molecule/app-bond

API

Interfaces

LogEntry

Structured log entry passed to transports, containing the level, message, timestamp, and optional context.

interface LogEntry {
  /**
   * Log level.
   */
  level: Exclude<LogLevel, 'silent'>

  /**
   * Log message.
   */
  message: string

  /**
   * Additional arguments.
   */
  args: unknown[]

  /**
   * Timestamp.
   */
  timestamp: Date

  /**
   * Logger name/namespace.
   */
  logger?: string

  /**
   * Additional context.
   */
  context?: Record<string, unknown>
}

LoggerConfig

Configuration for creating a logger instance.

interface LoggerConfig {
  /**
   * Minimum log level.
   */
  level?: LogLevel

  /**
   * Logger name/namespace.
   */
  name?: string

  /**
   * Additional transports (remote logging, file, etc.).
   */
  transports?: LogTransport[]

  /**
   * Whether to include timestamps in console output.
   */
  timestamps?: boolean

  /**
   * Custom log format function.
   */
  format?: (entry: LogEntry) => string

  /**
   * Default context to include with all logs.
   */
  context?: Record<string, unknown>
}

Logger

Logger instance with leveled logging methods, child logger creation, and transport management.

interface Logger {
  /**
   * Logs a trace message.
   */
  trace(message: string, ...args: unknown[]): void

  /**
   * Logs a debug message.
   */
  debug(message: string, ...args: unknown[]): void

  /**
   * Logs an info message.
   */
  info(message: string, ...args: unknown[]): void

  /**
   * Logs a warning message.
   */
  warn(message: string, ...args: unknown[]): void

  /**
   * Logs an error message.
   */
  error(message: string | Error, ...args: unknown[]): void

  /**
   * Sets the log level.
   */
  setLevel(level: LogLevel): void

  /**
   * Gets the current log level.
   */
  getLevel(): LogLevel

  /**
   * Creates a child logger with a namespace.
   */
  child(name: string, context?: Record<string, unknown>): Logger

  /**
   * Adds additional context to the logger.
   */
  withContext(context: Record<string, unknown>): Logger

  /**
   * Adds a transport.
   */
  addTransport(transport: LogTransport): () => void

  /**
   * Removes a transport.
   */
  removeTransport(transport: LogTransport): void
}

LoggerProvider

Logger provider interface that all logger bond packages must implement. Creates and manages logger instances and global log configuration.

interface LoggerProvider {
  /**
   * Gets a logger by name, or the root logger if no name given.
   */
  getLogger(name?: string): Logger

  /**
   * Creates a named logger.
   */
  createLogger(nameOrConfig: string | LoggerConfig, config?: LoggerConfig): Logger

  /**
   * Sets the global log level.
   */
  setLevel(level: LogLevel): void

  /**
   * Gets the global log level.
   */
  getLevel(): LogLevel

  /**
   * Adds a global transport.
   */
  addTransport(transport: LogTransport): () => void

  /**
   * Enables logging.
   */
  enable(): void

  /**
   * Disables logging.
   */
  disable(): void

  /**
   * Checks if logging is enabled.
   *
   * @returns `true` if logging is currently enabled.
   */
  isEnabled(): boolean
}

Types

LogLevel

Available log severity levels, ordered from most verbose (trace) to silent.

type LogLevel = 'trace' | 'debug' | 'info' | 'warn' | 'error' | 'silent'

LogTransport

Log transport function. Receives each log entry for custom processing (e.g. remote logging, file output, error tracking).

type LogTransport = (entry: LogEntry) => void

• entry — The log entry containing level, message, timestamp, and context.

Functions

createConsoleLogger(config)

Creates a console-based logger that outputs to console.* methods and dispatches entries to registered transports.

function createConsoleLogger(config?: LoggerConfig): Logger

• config — Logger configuration (level, name, transports, format).

Returns: A Logger instance backed by the browser/Node console.

createConsoleLoggerProvider(defaultLevel)

Creates a console-based logger provider with configurable log level, named child loggers, and pluggable transports.

function createConsoleLoggerProvider(defaultLevel?: LogLevel): LoggerProvider

• defaultLevel — The initial global log level (defaults to 'info').

Returns: A LoggerProvider backed by console output.

setProvider(provider)

Registers a logger provider as the active singleton.

function setProvider(provider: LoggerProvider): void

• provider — The logger provider implementation to bond.

getProvider()

Retrieves the bonded logger provider. If none is bonded, automatically creates and bonds a console-based provider with log level auto-detected from NODE_ENV ('debug' in development, 'info' otherwise).

function getProvider(): LoggerProvider

Returns: The active logger provider.

getLogger(name)

Retrieves a logger by name from the bonded provider. Returns the root logger if no name is given.

function getLogger(name?: string): Logger

• name — Optional logger name for scoped logging.

Returns: The named or root logger.

createLogger(nameOrConfig, config)

Creates a named logger with optional configuration via the bonded provider.

function createLogger(nameOrConfig: string | LoggerConfig, config?: LoggerConfig): Logger

• nameOrConfig — The logger name string, or a full LoggerConfig object.
• config — Optional configuration when the first argument is a name string.

Returns: A new named logger instance.

setLevel(level)

Sets the global log level on the bonded provider, affecting all loggers.

function setLevel(level: LogLevel): void

• level — The log level to set ('trace', 'debug', 'info', 'warn', 'error', or 'silent').

Returns: Nothing.

getLevel()

Returns the current global log level from the bonded provider.

function getLevel(): LogLevel

Returns: The active log level.

trace(message, args)

Logs a trace-level message via the root logger.

function trace(message: string, args?: unknown[]): void

• message — The log message string.
• args — Additional arguments to include in the log entry.

Returns: Nothing.

debug(message, args)

Logs a debug-level message via the root logger.

function debug(message: string, args?: unknown[]): void

• message — The log message string.
• args — Additional arguments to include in the log entry.

Returns: Nothing.

info(message, args)

Logs an info-level message via the root logger.

function info(message: string, args?: unknown[]): void

• message — The log message string.
• args — Additional arguments to include in the log entry.

Returns: Nothing.

warn(message, args)

Logs a warn-level message via the root logger.

function warn(message: string, args?: unknown[]): void

• message — The log message string.
• args — Additional arguments to include in the log entry.

Returns: Nothing.

error(message, args)

Logs an error-level message via the root logger.

function error(message: string | Error, args?: unknown[]): void

• message — The error message string or Error object.
• args — Additional arguments to include in the log entry.

Returns: Nothing.

defaultFormat(entry)

Default log format: "ISO_TIMESTAMP LEVEL[name]: message".

function defaultFormat(entry: LogEntry): string

• entry — The log entry to format.

Returns: The formatted log string.

createRemoteTransport(options)

Creates a remote logging transport that batches log entries and sends them to a remote endpoint via HTTP POST.

function createRemoteTransport(options: {
  url: string
  minLevel?: LogLevel
  batchSize?: number
  flushInterval?: number
  headers?: Record<string, string>
}): LogTransport

• options — Transport configuration.
• options.url — The remote endpoint URL to POST log batches to.
• options.minLevel — Minimum log level to send (default: 'warn').
• options.batchSize — Number of entries to buffer before flushing (default: 10).
• options.flushInterval — Milliseconds between automatic flushes (default: 5000).
• options.headers — Additional HTTP headers for the POST request.

Returns: A LogTransport function that buffers and sends entries.

Constants

LOG_LEVEL_PRIORITY

Log level priority (lower = more verbose).

const LOG_LEVEL_PRIORITY: Record<LogLevel, number>

Injection Notes

Requirements

Peer dependencies:

• @molecule/app-bond ^1.0.1

Runtime Dependencies

• @molecule/app-bond

• Log through this API, never bare console.log — levels, namespaces, and transports (remote error tracking) only apply to entries that flow through the logger. Every caught error is logged WITH the error object attached (or re-thrown) — never swallowed silently.

• getLogger('name') does NOT create a logger — it returns the ROOT logger unless createLogger('name') registered that name first. Create named loggers explicitly.

• Never log secrets, tokens, or PII. Entries reach the browser console and every registered transport — createRemoteTransport batches them to a remote HTTP endpoint, so a logged credential leaves the device.

• Remote delivery is best-effort by design (a failing transport is dropped silently to avoid log-failure recursion) — don't rely on transports for audit-grade trails.