log4js-node: The Familiar, Feature-Rich Logger for Node.js

Introduction to log4js-node: Java-inspired Logging for JavaScript Developers

For developers coming from Java or other log4j-compatible environments, the transition to Node.js logging becomes seamless with log4js-node. This powerful logging framework brings the familiar patterns and architecture of log4j to the JavaScript ecosystem, offering a comfortable yet powerful logging solution for Node.js applications.

Why log4js-node Remains a Popular Choice for Node.js Logging

log4js-node has maintained its position as a leading logging framework for several compelling reasons:

• Familiar Architecture: Based on the widely-used log4j pattern familiar to Java developers
• Comprehensive Appenders: Multiple output destinations including files, console, and network
• Flexible Layout Options: Customize log format with pattern layouts
• Log Levels: Standard hierarchy of logging levels (trace, debug, info, warn, error, fatal)
• Category Support: Organize logs by categories for better management
• Configuration Options: Configure via JavaScript objects or external configuration files
• Clustering Support: Special handling for Node.js cluster environments

Getting Started with log4js-node

Installation is simple with npm:

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npm install log4js

Basic usage requires minimal setup:

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const log4js = require('log4js');
log4js.configure({
  appenders: {
    console: { type: 'console' },
    file: { type: 'file', filename: 'logs/app.log' }
  },
  categories: {
    default: { appenders: ['console', 'file'], level: 'info' }
  }
});
const logger = log4js.getLogger();
logger.info('Application started');
// Category-specific loggers
const dbLogger = log4js.getLogger('database');
const authLogger = log4js.getLogger('auth');
dbLogger.info('Connected to database');
authLogger.warn('Failed login attempt');

Enhancing log4js-node with OpenTelemetry for Complete Observability

While log4js-node provides robust logging capabilities, modern applications benefit from a more integrated approach to observability. By combining log4js-node with an OpenTelemetry-native observability platform, you can transform isolated logs into components of a unified monitoring strategy.

This powerful integration enables:

• Trace Context Enrichment: Automatically add trace and span IDs to your log entries
• Log-Trace Correlation: Connect logs directly to distributed traces for context-rich debugging
• Cross-Service Visibility: Track requests across service boundaries with correlated logs
• Unified Monitoring: Manage logs, metrics, and traces through a single platform
• Advanced Analysis: Apply machine learning and analytics across all telemetry types

Implementing log4js-node with OpenTelemetry

Setting up the integration is straightforward:

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const opentelemetry = require('@opentelemetry/api');
const { NodeTracerProvider } = require('@opentelemetry/sdk-trace-node');
const log4js = require('log4js');
// Initialize OpenTelemetry
const provider = new NodeTracerProvider();
provider.register();
// Configure log4js with a custom layout that includes trace context
log4js.addLayout('json_with_trace', function() {
  return function(logEvent) {
    const span = opentelemetry.trace.getSpan(opentelemetry.context.active());
    if (span) {
      logEvent.data.traceId = span.spanContext().traceId;
      logEvent.data.spanId = span.spanContext().spanId;
    }
    return JSON.stringify(logEvent) + '\n';
  };
});
log4js.configure({
  appenders: {
    out: {
      type: 'stdout',
      layout: { type: 'json_with_trace' }
    }
  },
  categories: {
    default: { appenders: ['out'], level: 'info' }
  }
});
const logger = log4js.getLogger();
// Logs will now include trace context
logger.info('This log contains OpenTelemetry context');

Analyzing OpenTelemetry Logs in Dash0

Logs can be directly routed into Dash0. Dash0 with OpenTelemetry provides the ability to filter, search, group, and triage within a simple user interface, with full keyboard support. Dash0 also gives full log context by showing trace context, the call and resource that created the log - including details like the Kubernetes Pod, server, and cloud environment.

Log AI also enhanced the logs with more semantical metadata and structure without any manual pattern declaration.

Conclusion

In 2025, log4js-node continues to be a preferred choice for developers seeking a familiar, Java-inspired logging experience in Node.js. Its comprehensive feature set and flexible configuration options make it ideal for teams transitioning from other environments or requiring advanced logging capabilities.

By enhancing log4js-node with OpenTelemetry integration, developers can maintain these robust logging capabilities while gaining the advantages of unified observability. This combination delivers powerful insights by connecting logs with traces and metrics, enabling faster problem resolution and better application understanding.

For organizations that value the familiar log4j pattern while needing modern observability features, log4js-node with OpenTelemetry integration provides an ideal solution that leverages existing knowledge while embracing current best practices in application monitoring.