TypeScript Logger

A lightweight, flexible logging library for TypeScript/JavaScript applications with support for multiple log levels and printf-style formatting. This logger is mainly for use in CNIPS componenets using javascript/typescript.

CommonJS is not supported, this library is designed to be used with ES modules.

Features

• 🎯 Multiple Log Levels: Debug, Info, Warn, and Error
• 📝 Printf-style Formatting: Use format strings with arguments
• 🏷️ Application Tagging: Tag logs with application/component names
• ⏰ Automatic Timestamps: ISO 8601 formatted timestamps
• 💾 In-Memory Storage: Collect and retrieve logs programmatically
• 🎛️ Level Filtering: Only log messages at or above the configured level

Installation

npm install @cnips/logger

Quick Start

import { Logger, levels } from "@cnips/logger";

// Create a logger instance
const logger = new Logger("MyApp", levels.info);

// Log messages at different levels
logger.info("Application started");
logger.warn("This is a warning");
logger.error("Something went wrong");
logger.debug("Debug info"); // Won't be logged (below info level)

API Reference

Logger Class

Constructor

new Logger(app: string, level?: number)

• app: Application or component name (appears in log messages)
• level: Minimum log level (defaults to levels.info)

Methods

info(message: string, ...args: any[]): void

Logs an informational message.

logger.info("User %s logged in at %s", username, new Date().toISOString());

warn(message: string, ...args: any[]): void

Logs a warning message.

logger.warn("Low disk space: %d%% remaining", diskUsage);

error(message: string, ...args: any[]): void

Logs an error message.

logger.error("Failed to connect to database: %s", error.message);

debug(message: string, ...args: any[]): void

Logs a debug message.

logger.debug("Processing request with ID: %s", requestId);

getLogs(): string[]

Returns all logged messages as an array of strings.

const allLogs = logger.getLogs();
console.log(allLogs);

clearLogs(): void

Clears all stored log messages.

logger.clearLogs();

string(): string

Returns all logs as a single newline-separated string.

const logString = logger.string();
console.log(logString);

Log Levels

export const levels = {
    debug: -1,  // Most verbose
    info: 0,    // Default level
    warn: 1,    // Warnings only
    error: 2    // Errors only
}

Usage Examples

Basic Logging

import { Logger, levels } from "@cnips/logger";

const logger = new Logger("WebServer", levels.debug);

logger.debug("Server configuration loaded");
logger.info("Server starting on port 3000");
logger.warn("High memory usage detected");
logger.error("Failed to connect to database");

Printf-style Formatting

const logger = new Logger("UserService");

const userId = 12345;
const action = "login";
const timestamp = new Date().toISOString();

logger.info("User %d performed action '%s' at %s", userId, action, timestamp);
// Output: 2025-06-30T10:30:45.123Z [UserService] INFO User 12345 performed action 'login' at 2025-06-30T10:30:45.123Z

Log Level Filtering

// Only log warnings and errors
const logger = new Logger("CriticalService", levels.warn);

logger.debug("Debug message");  // Won't be logged
logger.info("Info message");    // Won't be logged  
logger.warn("Warning message"); // Will be logged
logger.error("Error message");  // Will be logged

Collecting and Processing Logs

const logger = new Logger("DataProcessor");

// Perform some operations
logger.info("Processing started");
logger.warn("Found %d invalid records", 5);
logger.info("Processing completed");

// Get all logs
const logs = logger.getLogs();
logs.forEach(log => console.log(log));

// Get logs as a single string
const logOutput = logger.string();
console.log(logOutput);

// Clear logs for next batch
logger.clearLogs();

Log Format

Each log message follows this format:

YYYY-MM-DDTHH:mm:ss.sssZ [AppName] LEVEL Message

Example:

2025-06-30T14:30:45.123Z [MyApp] INFO User authentication successful
2025-06-30T14:30:46.456Z [MyApp] WARN Rate limit approaching for user 12345
2025-06-30T14:30:47.789Z [MyApp] ERROR Database connection failed

TypeScript Support

This library is written in TypeScript and includes full type definitions. No additional @types packages are needed.