@2run/logger

Features

Installation

npm install @2run/logger
# or
yarn add @2run/logger
# or
pnpm add @2run/logger

Quick Start

Basic Usage

import { logger } from '@2run/logger';
// Simple logging
logger.info('Application started');
logger.debug('Debug information', { userId: 123 });
logger.warn('Warning message');
logger.error('Error occurred', { error: new Error('Something went wrong') });

Custom Logger with Configuration

import { createLogger, JSONFormatter, FileTransport } from '@2run/logger';
const logger = createLogger({
 prefix: 'MyApp',
 minLogLevel: 'info',
 maxHistory: 500,
 defaultMetadata: { appVersion: '1.0.0' },
});
logger.info('Configured logger ready');

JSON Logging (Structured Logs)

import { createLogger, JSONFormatter, ConsoleTransport } from '@2run/logger';
const logger = createLogger({
 transports: [new ConsoleTransport(new JSONFormatter())],
});
logger.info('User action', { userId: 123, action: 'login' });
// Output: {"timestamp":"2025-12-13T10:30:00.000Z","level":"info","message":"User action","id":"...","metadata":{"userId":123,"action":"login"}}

File Logging (Node.js)

import { createLogger, FileTransport } from '@2run/logger';
const logger = createLogger({
 transports: [
 new FileTransport({
 filePath: './logs/app.log',
 maxFileSize: 10 * 1024 * 1024, // 10MB
 maxFiles: 5,
 }),
 ],
});
logger.info('This will be written to file');

Multiple Transports

import { createLogger, ConsoleTransport, FileTransport, JSONFormatter } from '@2run/logger';
const logger = createLogger({
 transports: [
 new ConsoleTransport(), // Console output
 new FileTransport({ filePath: './logs/app.log' }), // File output
 new FileTransport(
 { filePath: './logs/app.json.log' },
 new JSONFormatter() // JSON file output
 ),
 ],
});
logger.info('Logged to console and two files');

Log Subscriptions

import { logger } from '@2run/logger';
// Subscribe to all log events
const unsubscribe = logger.subscribe((entry) => {
 console.log('Log event:', entry);
 // Send to analytics, remote logging service, etc.
});
logger.info('This will trigger the subscription');
// Unsubscribe when done
unsubscribe();

React Native Integration

import { createLogger } from '@2run/logger';
// Logger automatically detects React Native platform
const logger = createLogger({
 prefix: 'MyApp',
 platformInfo: true, // Includes iOS/Android version info
});
logger.info('Running on React Native');
// Output: [MyApp][INFO] Running on React Native [ios/14.5]

API Reference

createLogger(config?): Logger

Logger Methods

logger.debug(message, metadata?)

logger.info(message, metadata?)

logger.warn(message, metadata?)

logger.error(message, metadata?)

logger.getHistory(): LogEntry[]

logger.subscribe(listener): () => void

logger.flushToConsole()

logger.close(): Promise<void>

TypeScript Types

type LogLevel = 'debug' | 'info' | 'warn' | 'error';
interface LogEntry {
 id: string;
 level: LogLevel;
 message: string;
 metadata?: Record<string, unknown>;
 timestamp: number;
}
interface Transport {
 log(entry: LogEntry): void | Promise<void>;
 flush?(): void | Promise<void>;
 close?(): void | Promise<void>;
}
interface Formatter {
 format(entry: LogEntry, platformInfo?: PlatformInfo): string;
}

Examples

Example: Custom Transport

import { createLogger } from '@2run/logger';
import type { Transport, LogEntry } from '@2run/logger';
class RemoteTransport implements Transport {
 async log(entry: LogEntry) {
 await fetch('https://api.example.com/logs', {
 method: 'POST',
 body: JSON.stringify(entry),
 });
 }
}
const logger = createLogger({
 transports: [new RemoteTransport()],
});

Example: Conditional Logging

import { createLogger } from '@2run/logger';
const logger = createLogger({
 minLogLevel: process.env.NODE_ENV === 'production' ? 'warn' : 'debug',
});
// This will only log in development
logger.debug('Debug info');
// This will log in all environments
logger.error('Critical error');

Example: Correlation IDs

import { createLogger } from '@2run/logger';
import { v4 as uuidv4 } from 'uuid';
const logger = createLogger({
 correlationIdGenerator: () => uuidv4(),
});
logger.info('Request started'); // ID: abc-123-def
logger.info('Processing'); // ID: xyz-456-ghi

Performance Considerations

Best Practices

Contributing

License

Support