Console Transport Browser Server Deno Bun

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

Required Parameters

None - all parameters are optional.

Optional Parameters

Name	Type	Default	Description
level	"trace" | "debug" | "info" | "warn" | "error" | "fatal"	"trace"	Sets the minimum log level to process. Messages with a lower priority level will be ignored
appendObjectData	boolean	false	Controls where object data (metadata, context, errors) appears in the log messages. false: Object data appears as the first parameter. true: Object data appears as the last parameter. Has no effect if messageField is defined
messageField	string	-	If defined, places the message into the specified field in the log object, joins multi-parameter messages with a space (use the sprintf plugin for formatted messages), and only logs the object to the console
dateField	string	-	If defined, populates the field with the ISO date and adds it as an additional parameter to the console call. If dateFn is defined, will call dateFn to derive the date
levelField	string	-	If defined, populates the field with the log level and adds it as an additional parameter to the console call. If levelFn is defined, will call levelFn to derive the level
dateFn	() => string | number	-	If defined, a function that returns a string or number for the value to be used for the dateField
levelFn	(logLevel: LogLevelType) => string | number	-	If defined, a function that returns a string or number for a given log level. The input should be the logLevel
stringify	boolean	false	If true, applies JSON.stringify to the structured log output when messageField, dateField, or levelField is defined
messageFn	(params: LogLayerTransportParams) => string	-	Custom function to format the log message output. Receives log level, messages, and data; returns the formatted string

Examples

Level Configuration

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');

Object Data Positioning

// appendObjectData: false (default) - data appears first
const log = new LogLayer({
  transport: new ConsoleTransport({
    logger: console,
    appendObjectData: false
  })
});

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

// appendObjectData: true - data appears last
const log = new LogLayer({
  transport: new ConsoleTransport({
    logger: console,
    appendObjectData: true
  })
});

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

Message Field

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' })

Date Field

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

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

Level Field

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

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

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('User logged in', { timestamp: 1701437400000 })

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('User session expired', { level: 'WARN' })

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('Database connection failed', { level: 50 })

Stringify Output

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

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"}')

Custom Message Formatting

import { LogLayer, ConsoleTransport } from 'loglayer';
import type { LogLayerTransportParams } from 'loglayer';

const log = new LogLayer({
  transport: new ConsoleTransport({
    logger: console,
    messageFn: ({ logLevel, messages }: LogLayerTransportParams) => {
      return `[${logLevel.toUpperCase()}] ${messages.join(' ')}`;
    }
  })
});

log.info('User logged in');
// console.info('[INFO] User logged in')

log.warn('Connection unstable');
// console.warn('[WARN] Connection unstable')

Prefix behavior

If you use withPrefix(), the prefix is applied to the messages before they reach messageFn. For example, log.withPrefix('[MyApp]').info('Hello') would pass messages: ['[MyApp] Hello'] to your messageFn.

Structured Logging

TIP

If you want structured logging enabled by default without manual configuration, use the Structured Transport instead.

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