@feizk/logger

A lightweight, pluggable logger with colored outputs, structured logging, and transport support.

Features

• 🚀 Zero dependencies - No external runtime dependencies
• 🎨 Colored output - ANSI color codes for terminal output
• 📊 6 log levels - trace, debug, info, warn, error, fatal
• 📝 Structured logging - JSON mode for production environments
• 🔌 Pluggable transports - Add custom transports (files, databases, etc.)
• 👶 Child loggers - Create prefixed loggers with merged context
• ⏱️ Custom timestamps - Presets (iso, locale) or custom format
• 🎯 Type-safe - Full TypeScript support

Installation

npm install @feizk/logger

Usage

import { Logger } from '@feizk/logger';

const logger = new Logger();

logger.info('Hello, world!');
logger.warn('This is a warning');
logger.error('This is an error');
logger.debug('Debug information');
logger.trace('Very detailed trace');
logger.fatal('Critical error!');

Options

| Option | Type | Default | Description | | -------------- | -------------------------------------------------------------- | ----------- | ---------------------------- | | level | 'trace' \| 'debug' \| 'info' \| 'warn' \| 'error' \| 'fatal' | 'debug' | Minimum log level to output | | silent | boolean | false | Suppress all console output | | enableColors | boolean | true | Enable colored output | | timestamp | 'iso' \| 'locale' \| (date: Date) => string | 'iso' | Timestamp format | | json | boolean | false | Output logs as JSON | | formatter | (entry: LogEntry) => string | undefined | Custom log formatter | | transports | Transport[] | [] | Initial transports to attach | | prefix | string | undefined | Prefix for all log messages | | context | Record<string, unknown> | {} | Initial context metadata |

API

Logger Methods

• trace(...args) - Log a trace message (most verbose)
• debug(...args) - Log a debug message
• info(...args) - Log an info message
• warn(...args) - Log a warning message
• error(...args) - Log an error message
• fatal(...args) - Log a fatal message (most severe)
• setLevel(level) - Set the minimum log level
• getLevel() - Get the current log level
• addTransport(transport) - Add a custom transport
• removeTransport(transport) - Remove a transport
• child(options) - Create a child logger
• destroy() - Destroy the logger and all transports

Log Levels

Logs are filtered by severity. The order from least to most severe:

1. trace - Very detailed debugging information
2. debug - Detailed information for debugging
3. info - General informational messages
4. warn - Warning conditions
5. error - Error conditions
6. fatal - Critical errors

Advanced Usage

Custom Timestamp

const logger = new Logger({
  timestamp: 'locale', // or 'iso' (default)
});

// Custom format
const logger = new Logger({
  timestamp: (date) => date.toISOString(),
});

Custom Formatter

const logger = new Logger({
  formatter: (entry) =>
    `[${entry.timestamp}] [${entry.level.toUpperCase()}] ${entry.args.join(' ')}`,
});

JSON Structured Logging

const logger = new Logger({ json: true });
logger.info('User logged in', { userId: '123' });
// Output: {"level":"info","timestamp":"2024-01-01T00:00:00.000Z","message":"User logged in","context":{"userId":"123"}}

Child Logger

const parent = new Logger({ prefix: 'app', context: { version: '1.0.0' } });

const child = parent.child({
  prefix: 'api',
  context: { endpoint: '/users' },
});

child.info('Request received');
// Output includes prefix "app:api" and merged context

Pluggable Transports

import { Logger, type Transport, type LogEntry } from '@feizk/logger';

// Create a custom transport
class FileTransport implements Transport {
  private stream: WriteStream;

  constructor(path: string) {
    this.stream = createWriteStream(path);
  }

  log(entry: LogEntry): void {
    this.stream.write(JSON.stringify(entry) + '\n');
  }

  destroy(): void {
    this.stream.end();
  }
}

// Use the transport
const logger = new Logger();
logger.addTransport(new FileTransport('/var/log/app.log'));
logger.info('This will be logged to the file');

Migration from v1.x

Discord Transport

Discord transport has been moved to a separate package. Use @feizk/logger-discord instead:

// v1.x
const logger = new Logger({
  discord: { enable: true, webhookURL: '...' },
});

// v2.x
import { Logger } from '@feizk/logger';
import { DiscordTransport } from '@feizk/logger-discord';

const logger = new Logger();
logger.addTransport(new DiscordTransport({ webhookURL: '...' }));

Removed Options

• discord - Use @feizk/logger-discord instead
• formatTimestamp - Use timestamp instead
• formatLog - Use formatter instead

License

MIT