< log - A Flexible and Powerful Logger for TypeScript

< log is a versatile logging library for TypeScript designed to support both JSON and plain-text logging formats. It provides colorized output in plain-text mode and supports structured logs in JSON format with contextual data.

Features

• Supports two modes: JSON and plain-text
• Colorized logs for different log levels in plain-text mode
• Structured logging with context fields in JSON mode
• Configurable log levels: debug, info, warn, error, fatal
• Easy to integrate and lightweight

Installation

You can install the library using npm or Yarn:

npm install log

or

yarn add log

Usage

1. Basic Setup:

Here is a basic example of how to use < log:

import Logger, { LogLevel, LogMode } from '<log>';

// Create a logger with JSON output
const jsonLogger = new Logger(LogLevel.Info, LogMode.Json);
jsonLogger.info('User login successful', { userId: 123 });

// Create a logger with colored plain-text output
const plainLogger = new Logger(LogLevel.Info, LogMode.Plain);
plainLogger.info('User logged out', { userId: 456 });

2. Log Levels:

< log supports five log levels, which can be used to filter logs based on severity:

• debug: Detailed information typically useful only during development.
• info: General information about app behavior.
• warn: An indication that something unexpected happened, but the app is still functioning.
• error: A problem that requires attention.
• fatal: A critical problem that will cause the app to stop functioning.

Example:

plainLogger.debug('This is a debug message');
plainLogger.info('This is an info message');
plainLogger.warn('This is a warning');
plainLogger.error('An error occurred');
plainLogger.fatal('A fatal error occurred');

3. Contextual Logging

You can add contextual data to your logs, which will appear as structured fields in JSON mode and as key-value pairs in plain-text mode.

jsonLogger.info('Fetching user details', { userId: 789, action: 'fetch' });
plainLogger.error('Failed to fetch user details', { userId: 789, errorCode: 500 });

JSON Output Example:

{
  "timestamp": "2024-09-21T12:00:00.000Z",
  "level": "info",
  "message": "Fetching user details",
  "context": {
    "userId": 789,
    "action": "fetch"
  }
}

Plain-text Output Example:

[2024-09-21T12:00:00.000Z] [INFO] Fetching user details | userId: 789, action: fetch

4. Configuration:

• Log Levels:
  The log level can be configured when creating a Logger instance. Logs below the specified level will be ignored.

const logger = new Logger(LogLevel.Warn, LogMode.Plain);
// This will not log since it's below the Warn level
logger.info('This will not be logged');

• Log Modes:
  < log supports two log modes:

1. JSON: Structured logging, with each message and context serialized as JSON.
2. Plain-text: Colorized logs with key-value pairs for context.

const logger = new Logger(LogLevel.Info, LogMode.Json);

5. Colored Output for Plain-text

Log levels are colorized for easier reading in plain-text mode:

• debug: Magenta
• info: Blue
• warn: Yellow
• error: Red
• fatal: White text on a red background