@guiiai/logg

Yet another simple, nearly zero dependency, structural log compliance logger implementation.

Features

• 🛠️ Stack Parse: Automatically captures and includes stack trace information for enhanced debugging
• 📞 Caller Records: Provides detailed information about the calling function and file with clickable hyperlinks
• 🗄️ JSON Format & stdout: Outputs logs in JSON format to stdout for easy parsing and integration with log management tools
• 🎨 Pretty Format: Beautiful colored output for development with browser console support
• 🔄 Drop-in Replacement: Can be used as a direct replacement for popular loggers like Winston
• 📏 Best Practices: Implements industry best practices for structured logging
• 🧩 Intuitive API: Simple and easy-to-use fluent API for quick integration
• 🌐 Universal: Works in both Node.js and browser environments
• ⚡ Zero Config: Works out of the box with sensible defaults

Preview

Installation

npm install @guiiai/logg

Quick Start

import { initLogger, useGlobalLogger } from '@guiiai/logg'

// Initialize with defaults (Verbose level, Pretty format)
initLogger()

// Create a logger and start logging
const log = useGlobalLogger('MyApp')
log.log('Hello world!')

Usage Examples

Basic Usage

import { createLogg, Format, LogLevel, setGlobalFormat, setGlobalLogLevel } from '@guiiai/logg'

setGlobalLogLevel(LogLevel.Debug)
setGlobalFormat(Format.Pretty) // Otherwise it will output JSON

// Create a logger instance with a specific context
const log = createLogg('http/request').useGlobalConfig()

// Log messages with different levels
log.debug('Debugging info')
log.log('Regular log')
log.warn('Warning message')
log.error('Error occurred')

Adding Custom Fields

// Add single field
log
  .withField('requestId', req.id)
  .withField('url', req.url)
  .error('Resource not found (404)')

// Add multiple fields at once
log
  .withFields({
    userId: '12345',
    ip: '192.168.1.1',
    userAgent: 'Mozilla/5.0'
  })
  .log('User logged in')

Error Handling

try {
  // Some operation
} catch (err) {
  // Automatically extracts error message, stack trace, and cause
  log.withError(err).error('Operation failed')

  // Or use errorWithError for more control
  log.errorWithError('Failed to process request', err)
}

Child Loggers

const parentLog = createLogg('app').useGlobalConfig()

// Create child logger with persistent fields
const childLog = parentLog.child({
  module: 'database',
  version: '1.0.0'
})

// All logs from childLog will include the parent fields
childLog.log('Connected to database')

Auto-Context Logger

import { createLogger } from '@guiiai/logg'

// Automatically includes file path and line number with clickable hyperlinks
const log = createLogger().useGlobalConfig()
log.log('This log knows where it came from!')

Custom Time Format

const log = createLogg('app')
  .useGlobalConfig()
  .withTimeFormatter((date) => {
    return date.toLocaleString('en-US', {
      timeZone: 'America/New_York'
    })
  })

log.log('Log with custom timestamp')

Error Processing

// Transform errors before logging
const log = createLogg('app')
  .useGlobalConfig()
  .withErrorProcessor((err) => {
    if (err instanceof CustomError) {
      // Add custom properties or transform the error
      return { ...err, customField: 'value' }
    }
    return err
  })

log.withError(someError).error('Processed error')

API Reference

Logger Factory Functions

createLogg(context: string): Logg

Creates a new logger instance with the specified context.

const log = createLogg('MyModule')

createLogger(context?: string): Logg

Creates a logger with automatic context from the call site (file path and line number). Includes clickable hyperlinks in supported terminals.

const log = createLogger() // Context is auto-generated
const log2 = createLogger('CustomContext') // Override with custom context

createGlobalLogger(context?: string): Logg

Creates a logger with automatic context and applies global configuration.

const log = createGlobalLogger()

initLogger(level?: LogLevel, format?: Format): void

Initializes global logger configuration with defaults.

import { initLogger, LogLevel, Format } from '@guiiai/logg'

initLogger(LogLevel.Verbose, Format.Pretty)

Aliases:

• useLogg → createLogg
• useLogger → createLogger
• useGlobalLogger → createGlobalLogger

Logger Instance Methods

Configuration Methods

• useGlobalConfig(): Logg - Applies global configuration to the logger instance
• child(fields?: Record<string, any>): Logg - Creates a child logger with additional persistent fields
• withContext(context: string): Logg - Sets context dynamically (returns cloned instance)
• withLogLevel(logLevel: LogLevel): Logg - Sets log level dynamically (returns cloned instance)
• withLogLevelString(logLevelString: LogLevelString): Logg - Sets log level using string (returns cloned instance)
• withFormat(format: Format): Logg - Sets output format dynamically (returns cloned instance)
• withFields(fields: Record<string, any>): Logg - Alias for child()
• withField(key: string, value: any): Logg - Adds a single custom field
• withError(err: Error | unknown): Logg - Attaches error object with automatic extraction of message, stack, and cause
• withCallStack(errorLike: { message: string, stack?: string }): Logg - Adds call stack information
• withTimeFormatter(fn: (date: Date) => string): Logg - Sets custom time formatter function
• withErrorProcessor(fn: (err: Error | unknown) => Error | unknown): Logg - Sets custom error processor function

Logging Methods

• debug(message: any, ...optionalParams: any[]): void - Logs debug-level message
• verbose(message: any, ...optionalParams: any[]): void - Logs verbose-level message
• log(message: any, ...optionalParams: any[]): void - Logs info-level message
• warn(message: any, ...optionalParams: any[]): void - Logs warning-level message
• error(message: any, stack?: string, ...optionalParams: any[]): void - Logs error-level message
• errorWithError(message: any, err: Error | unknown, ...optionalParams: any[]): void - Logs error with automatic error extraction

Global Configuration

Log Level

import { getGlobalLogLevel, setGlobalLogLevel, LogLevel } from '@guiiai/logg'

setGlobalLogLevel(LogLevel.Debug)
const level = getGlobalLogLevel()

// Or use string-based methods
import { setGlobalLogLevelString, getGlobalLogLevelString } from '@guiiai/logg'

setGlobalLogLevelString('debug')
const levelString = getGlobalLogLevelString()

Format

import { getGlobalFormat, setGlobalFormat, Format } from '@guiiai/logg'

setGlobalFormat(Format.Pretty)
const format = getGlobalFormat()

Time Formatter

import { setGlobalTimeFormatter, getGlobalTimeFormatter } from '@guiiai/logg'

setGlobalTimeFormatter((date) => date.toISOString())
const formatter = getGlobalTimeFormatter()

Enums and Types

LogLevel

enum LogLevel {
  Error = 0,
  Warning = 1,
  Log = 2,
  Verbose = 3,
  Debug = 4
}

LogLevelString

type LogLevelString = 'error' | 'warn' | 'log' | 'verbose' | 'debug'

Format

enum Format {
  JSON = 'json',
  Pretty = 'pretty'
}

Configuration

Log Levels

Log levels control which messages are output. Higher levels include all lower levels.

Level	Value	Description
Error	0	Only error messages
Warning	1	Errors and warnings
Log	2	Errors, warnings, and general logs
Verbose	3	All above plus verbose information
Debug	4	All messages including debug info

Output Formats

JSON Format

Structured JSON output, ideal for production environments and log aggregation tools.

{"level":"log","context":"app","timestamp":"2024-01-01T00:00:00.000Z","message":"User logged in","fields":{"userId":"123"}}

Pretty Format

Human-readable colored output for development. Automatically detects browser environments and adjusts output accordingly.

[2024-01-01 00:00:00] LOG app: User logged in { userId: '123' }

Environment Support

Node.js

Full support for all features including:

• Terminal hyperlinks (VS Code, iTerm2, etc.)
• Colored output
• Stack trace parsing

Browser

Optimized browser support with:

• Console-friendly output
• Proper object expansion in browser devtools
• Automatic format detection

Why @guiiai/logg?

• Lightweight: Minimal dependencies (only 3 runtime deps)
• Type-safe: Full TypeScript support with complete type definitions
• Flexible: Works in any environment without configuration
• Developer-friendly: Beautiful output and clickable source links
• Production-ready: JSON output for log aggregation systems

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Contributors

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