Console Transport

The simplest integration is with the built-in console object, which is available in both Node.js and browser environments.

Transport Source

Installation

No additional packages needed beyond the core loglayer package:

npm

npm i loglayer

pnpm

pnpm add loglayer

yarn

yarn add loglayer

Setup

import { LogLayer, ConsoleTransport } from 'loglayer'

const log = new LogLayer({
  transport: new ConsoleTransport({
    logger: console,
    // Optional: control where object data appears in log messages
    appendObjectData: false // default: false - object data appears first
  })
})

Configuration Options

level

Sets the minimum log level to process. Messages with a lower priority level will be ignored.

• Type: "trace" | "debug" | "info" | "warn" | "error" | "fatal"
• Default: "trace" (processes all log levels)

Example with minimum level set to "info":

const log = new LogLayer({
  transport: new ConsoleTransport({
    logger: console,
    level: "info"  // Will only process info, warn, error, and fatal logs
  })
});

log.debug('This message will be ignored');
log.info('This message will be logged');

appendObjectData

Controls where object data (metadata, context, errors) appears in the log messages:

• false (default): Object data appears as the first parameter
• true: Object data appears as the last parameter

Has no effect if messageField is defined.

Example with appendObjectData: false (default):

log.withMetadata({ user: 'john' }).info('User logged in');
// console.info({ user: 'john' }, 'User logged in')

Example with appendObjectData: true:

log.withMetadata({ user: 'john' }).info('User logged in');
// console.info('User logged in', { user: 'john' })

messageField

If defined, this option will:

• Place the message into the specified field in the log object
• Join multi-parameter messages with a space (use the sprintf plugin for formatted messages)
• Only log the object to the console

Example with messageField: 'msg':

const log = new LogLayer({
  transport: new ConsoleTransport({
    logger: console,
    messageField: 'msg'
  })
});

log.withMetadata({ user: 'john' }).info('User logged in', 'successfully');
// console.info({ user: 'john', msg: 'User logged in successfully' })

dateField

If defined, populates the field with the ISO date. If dateFn is defined, will call dateFn to derive the date.

• Type: string
• Default: undefined

Example with dateField: 'timestamp':

const log = new LogLayer({
  transport: new ConsoleTransport({
    logger: console,
    dateField: 'timestamp'
  })
});

log.info('User logged in');
// console.info({ timestamp: '2023-12-01T10:30:00.000Z' })

levelField

If defined, populates the field with the log level. If levelFn is defined, will call levelFn to derive the level.

• Type: string
• Default: undefined

Example with levelField: 'level':

const log = new LogLayer({
  transport: new ConsoleTransport({
    logger: console,
    levelField: 'level'
  })
});

log.warn('User session expired');
// console.warn({ level: 'warn' })

dateFn

If defined, a function that returns a string or number for the value to be used for the dateField.

• Type: () => string | number
• Default: undefined

Example with custom date function:

const log = new LogLayer({
  transport: new ConsoleTransport({
    logger: console,
    dateField: 'timestamp',
    dateFn: () => Date.now() // Returns Unix timestamp
  })
});

log.info('User logged in');
// console.info({ timestamp: 1701437400000 })

levelFn

If defined, a function that returns a string or number for a given log level. The input should be the logLevel.

• Type: (logLevel: LogLevelType) => string | number
• Default: undefined

Example with custom level function:

const log = new LogLayer({
  transport: new ConsoleTransport({
    logger: console,
    levelField: 'level',
    levelFn: (level) => level.toUpperCase()
  })
});

log.warn('User session expired');
// console.warn({ level: 'WARN' })

Example with numeric level mapping:

const log = new LogLayer({
  transport: new ConsoleTransport({
    logger: console,
    levelField: 'level',
    levelFn: (level) => {
      const levels = { trace: 10, debug: 20, info: 30, warn: 40, error: 50, fatal: 60 };
      return levels[level as keyof typeof levels] || 0;
    }
  })
});

log.error('Database connection failed');
// console.error({ level: 50 })

Combining Fields

You can combine multiple fields to create structured log objects:

const log = new LogLayer({
  transport: new ConsoleTransport({
    logger: console,
    messageField: 'msg',
    dateField: 'timestamp',
    levelField: 'level'
  })
});

log.withMetadata({ user: 'john' }).info('User logged in');
// console.info({ 
//   user: 'john', 
//   msg: 'User logged in', 
//   timestamp: '2023-12-01T10:30:00.000Z', 
//   level: 'info' 
// })

Log Level Mapping

LogLayer	Console
trace	debug
debug	debug
info	info
warn	warn
error	error
fatal	error