Logger

A lightweight, colorful, and feature-rich JavaScript logger with a beautiful interface and powerful functionality.

Features

• ✨ Multiple Log Levels: TRACE, DEBUG, INFO, WARN, ERROR, SILENT
• 🎨 Colored Output: Enhanced color support for both browsers and terminals
• 🔀 Level Filtering: Disable logs below a certain level
• 📝 Named Loggers: Support for module-specific loggers
• 💾 Level Persistence: Save settings between sessions
• ⏲ Timestamps: Configurable timestamp output
• 🔌 Formatters: Multiple output formats available
• 🚀 Lightweight & Fast: Under 5KB minified and gzipped
• 📱 Universal Support: First-class support for ESM and CommonJS
• 💻 TypeScript Ready: Comprehensive TypeScript definitions

Installation

npm install logger

Quick Start

ESM (ECMAScript Modules)

// Modern ES module import
import logger from 'logger';

// Basic usage
logger.info('Application started');
logger.warn('Configuration missing, using defaults');
logger.error('Failed to connect to database', { host: 'localhost', port: 5432 });

CommonJS

// CommonJS require
const logger = require('logger');

// Basic usage
logger.info('Application started');
logger.warn('Configuration missing, using defaults');
logger.error('Failed to connect to database', { host: 'localhost', port: 5432 });

Named Loggers

// Module specific logger
const apiLogger = logger.getLogger('api');
apiLogger.setLevel('debug');
apiLogger.debug('Request received', { method: 'GET', path: '/users' });

// Customize output
logger
  .setLevel('info')     // Only show info and above
  .useColors(true)      // Enable colors
  .useTimestamps(true)  // Show timestamps
  .persist();           // Save settings to localStorage/cookies

Log Levels

The following log levels are available, in order of verbosity:

• TRACE (0): Most verbose, for detailed debugging
• DEBUG (1): Debug information
• INFO (2): General information
• WARN (3): Warnings (default level)
• ERROR (4): Errors
• SILENT (5): No logging

Colored Output

Logger supports colorized output across environments:

| Level | Browser | Terminal | Description | |-------|---------|----------|-------------| | TRACE | Cyan | Cyan | Detailed tracing information | | DEBUG | Green | Green | Debug-level messages | | INFO | Blue | Bright Blue | Informational messages | | WARN | Orange | Yellow | Warning messages | | ERROR | Red | Bright Red | Error messages |

Colors are automatically enabled based on environment detection and can be toggled with:

// Enable colors
logger.useColors(true);

// Disable colors
logger.useColors(false);

API Reference

Logger Methods

• logger.trace(...args): Log at TRACE level
• logger.debug(...args): Log at DEBUG level
• logger.info(...args): Log at INFO level
• logger.warn(...args): Log at WARN level
• logger.error(...args): Log at ERROR level
• logger.log(...args): Alias for debug

Configuration

• logger.setLevel(level, persist?): Set the current log level
• logger.getLevel(): Get the current log level as enum
• logger.getLevelName(): Get the current log level name
• logger.setDefaultLevel(level): Set the default log level
• logger.resetLevel(): Reset to the default log level
• logger.enableAll(persist?): Enable all logging (TRACE)
• logger.disableAll(persist?): Disable all logging (SILENT)
• logger.useColors(enable): Enable or disable colors
• logger.useTimestamps(enable): Enable or disable timestamps
• logger.persist(storage?): Enable log level persistence

Named Loggers

• logger.getLogger(name): Get a named logger
• logger.getLoggers(): Get all named loggers

Formatters

• logger.setFormatter(formatter): Set custom formatter
• logger.getFormatter(): Get current formatter

Custom Formatters

The library includes several built-in formatters:

• DefaultFormatter: Includes timestamps, log level, and logger name
• MinimalFormatter: Simple prefix with just the logger name
• JsonFormatter: Structured JSON output

Example:

// ESM
import logger, { JsonFormatter } from 'logger';

// CommonJS
const { default: logger, JsonFormatter } = require('logger');

// Create a JSON formatter
const jsonFormatter = new JsonFormatter();

// Use it with the logger
logger.setFormatter(jsonFormatter);

// Or with a named logger
const apiLogger = logger.getLogger('api');
apiLogger.setFormatter(jsonFormatter);

You can create your own formatter by implementing the LogFormatter interface.

Module Compatibility

This logger provides first-class support for both ESM and CommonJS module systems:

ESM (ECMAScript Modules)

// Default import
import logger from 'logger';

// Named imports
import logger, { LogLevel, JsonFormatter } from 'logger';

CommonJS

// Direct require (default export)
const logger = require('logger');

// Destructured require
const { default: logger, JsonFormatter } = require('logger');

Browser Usage

Logger works great in browsers and includes automatic persistence using localStorage or cookies.

<script type="module">
  import logger from 'logger';
  logger.info('Logger loaded in browser');
  
  // Get a module-specific logger
  const uiLogger = logger.getLogger('ui');
  uiLogger.debug('UI component initialized');
</script>

Node.js Usage

Use the logger in Node.js applications:

// ESM
import logger from 'logger';
logger.info('Node.js application started');

// CommonJS
const logger = require('logger');
logger.info('Node.js application started');

// Named loggers work the same
const dbLogger = logger.getLogger('database');
dbLogger.info('Connected to database');

Examples

Check out the included examples:

• example.cjs - CommonJS example
• example.mjs - ES Modules example

Run them with:

# Build the library first
npm run build

# Run examples
npm run example:cjs
npm run example:esm

License

MIT