Logger Module

Overview

This logger module provides a flexible and configurable logging mechanism for Node.js applications. It supports different log levels, custom log domains, and allows customization of the log output and format. It uses chalk for colored console output and ensures that only one instance of the logger is created (singleton pattern).

Usage

Importing the Logger

import Logger, { LogLevel } from "./logger";

Getting the Logger Instance

To get the singleton instance of the logger, use:

const logger = Logger.getInstance();

Setting Logger Options

You can set options like log level, log domains, custom output function, and custom format function when getting the instance:

const logger = Logger.getInstance({
  logLevel: LogLevel.DEBUG,
  logDomains: ["APP", "DB"],
  customOutput: (logMessage) => {
    // Custom output logic
    console.log(logMessage);
  },
  customFormat: (level, domain, message) => {
    // Custom format logic
    return {
      level,
      domain,
      message,
      timestamp: new Date().toISOString(),
    };
  },
});

Logging Messages

The logger supports different log levels:

• INFO
• WARN
• ERROR
• DEBUG

You can log messages using the corresponding methods:

logger.info("APP", "This is an info message");
logger.warn("APP", "This is a warning message");
logger.error("APP", "This is an error message");
logger.debug("APP", "This is a debug message");

Example

import Logger, { LogLevel } from "./logger";

const logger = Logger.getInstance({
  logLevel: LogLevel.DEBUG,
  logDomains: ["APP", "DB"],
});

logger.info("APP", "Application has started");
logger.warn("DB", "Database connection is slow");
logger.error("APP", "Unhandled exception occurred");
logger.debug("DB", "Query executed: SELECT * FROM users");

Logger Options

logLevel

• Specifies the minimum level of messages to log.
• Type: LogLevel
• Default: LogLevel.INFO

logDomains

• Specifies the domains to log messages for.
• Type: string[]
• Default: [] (log all domains)

customOutput

• Custom function for handling the log output.
• Type: (logMessage: LogMessage, ...additionalArgs: any[]) => void

customFormat

• Custom function for formatting log messages.
• Type: (level: LogLevel, domain: LogDomain, message: string, ...additionalArgs: any[]) => LogMessage

Log Levels

export enum LogLevel {
  NONE = "none",
  INFO = "info",
  WARN = "warn",
  ERROR = "error",
  DEBUG = "debug",
}

API Reference

Logger.getInstance(options?: LoggerOptions): Logger

Returns the singleton instance of the logger, optionally configuring it with the provided options.

Logger.resetInstance(): void

Resets the logger instance. Useful for testing purposes.

Logger.log(level: LogLevel, domain: LogDomain, message: string, ...additionalArgs: any[]): void

Logs a message with the specified level and domain.

Logger.info(domain: LogDomain, message: string, ...additionalArgs: any[]): void

Logs an info message.

Logger.warn(domain: LogDomain, message: string, ...additionalArgs: any[]): void

Logs a warning message.

Logger.error(domain: LogDomain, message: string, ...additionalArgs: any[]): void

Logs an error message.

Logger.debug(domain: LogDomain, message: string, ...additionalArgs: any[]): void

Logs a debug message.

Testing

The logger module includes tests to ensure its functionality. The tests cover creating singleton instances, respecting log levels and domains, and using custom output and format functions.