@sylphx/cat

The fastest, lightest, and most extensible logger for JavaScript

1.97 KB • Zero dependencies • Universal runtime support

Installation

npm install @sylphx/cat

Description

@sylphx/cat is a blazing-fast, minimal logger designed for all JavaScript runtimes. It provides structured JSON logging with automatic error serialization, type-safe APIs, and extensibility through formatters, transports, and plugins.

Perfect for CLIs, APIs, microservices, and any application where performance and bundle size matter.

Usage Examples

Basic Logging

import { createLogger } from '@sylphx/cat'

const logger = createLogger()

logger.info('Server started', { port: 3000 })
// {"level":"info","timestamp":1700000000000,"message":"Server started","data":{"port":3000}}

logger.error('Connection failed', { host: 'db.example.com' })
// {"level":"error","timestamp":1700000000000,"message":"Connection failed","data":{"host":"db.example.com"}}

Error Serialization

Errors are automatically serialized with full stack traces:

import { createLogger, stdSerializers } from '@sylphx/cat'

const logger = createLogger({
  serializers: stdSerializers
})

try {
  throw new Error('Database connection failed')
} catch (err) {
  logger.error('Failed to connect', { err })
  // {"level":"error","message":"Failed to connect","err":{"message":"Database connection failed","stack":"..."}}
}

Child Loggers with Context

const logger = createLogger({ context: { service: 'api' } })
const requestLogger = logger.child({ requestId: 'abc-123' })

requestLogger.info('Processing request')
// {"level":"info","message":"Processing request","context":{"service":"api","requestId":"abc-123"}}

Custom Log Levels

const logger = createLogger({ level: 'warn' })

logger.debug('This will not be logged')
logger.warn('This will be logged')
logger.error('This will also be logged')

API Reference

Core Exports

createLogger(options?: LoggerOptions): Logger

Creates a new logger instance.

Options:

• level?: LogLevel - Minimum log level (default: 'info')
• formatter?: Formatter - Log formatter (default: JSON)
• transports?: Transport[] - Output transports (default: console)
• plugins?: Plugin[] - Logger plugins
• context?: Record<string, unknown> - Global context
• batch?: boolean - Enable batching (default: false)
• batchSize?: number - Batch size (default: 100)
• batchInterval?: number - Batch interval in ms (default: 1000)

Logger Interface

Main logging methods:

• trace(message: string, data?: Record<string, unknown>): void
• debug(message: string, data?: Record<string, unknown>): void
• info(message: string, data?: Record<string, unknown>): void
• warn(message: string, data?: Record<string, unknown>): void
• error(message: string, data?: Record<string, unknown>): void
• fatal(message: string, data?: Record<string, unknown>): void

Utility methods:

• setLevel(level: LogLevel): void
• child(context: Record<string, unknown>): Logger
• flush(): Promise<void>
• close(): Promise<void>

Built-in Formatters

jsonFormatter(): Formatter

Default JSON formatter (already included in core).

import { createLogger, jsonFormatter } from '@sylphx/cat'

const logger = createLogger({
  formatter: jsonFormatter()
})

Built-in Transports

consoleTransport(): Transport

Default console transport (already included in core).

import { createLogger, consoleTransport } from '@sylphx/cat'

const logger = createLogger({
  transports: [consoleTransport()]
})

Built-in Serializers

stdSerializers

Standard serializers including automatic error serialization.

import { createLogger, stdSerializers } from '@sylphx/cat'

const logger = createLogger({
  serializers: stdSerializers
})

Available serializers:

• err / error - Serializes Error objects with stack traces

serializeError(err: Error): SerializedError

Manually serialize an error object.

import { serializeError } from '@sylphx/cat'

const serialized = serializeError(new Error('Something went wrong'))
// { message: 'Something went wrong', stack: '...', name: 'Error' }

Package Size

• Minified: ~6 KB
• Minified + Gzipped: 1.97 KB
• Zero dependencies

Links

• Main Documentation
• GitHub Repository
• npm Package
• API Reference

Related Packages

• @sylphx/cat-pretty - Pretty formatter for development
• @sylphx/cat-file - File and stream transports
• @sylphx/cat-http - HTTP request/response serializers
• @sylphx/cat-otlp - OpenTelemetry Protocol export
• @sylphx/cat-tracing - W3C Trace Context support
• @sylphx/cat-redaction - PII/sensitive data redaction
• @sylphx/cat-tail-sampling - Intelligent cost-saving sampling

License

MIT © Kyle Zhu