Log4js is a popular logging framework for Node.js applications, which allows you to generate and control logs in your application. While Log4js provides default logging capabilities, it also offers a real-time logging feature that allows you to view logs as they are being generated.

In this blog post, we will explore how to implement real-time logging using Log4js in Node.js.

Installation

First, we need to install the Log4js package using npm:

$ npm install log4js

Setting up Log4js

After installing Log4js, we can create a file called logger.js where we will define our logging configuration.

// logger.js
const log4js = require('log4js');

log4js.configure({
  appenders: {
    console: { type: 'console' },
    file: { type: 'file', filename: 'logs/all.log' }
  },
  categories: {
    default: { appenders: ['console', 'file'], level: 'debug' }
  }
});

const logger = log4js.getLogger();

module.exports = logger;

In the configuration above, we define two appenders: ‘console’ and ‘file’. The ‘console’ appender allows logs to be displayed in the console, while the ‘file’ appender writes logs to a file named all.log. We also specify the logging level as ‘debug’, which means it will log all levels from ‘debug’ to ‘fatal’.

Logging in real-time

To implement real-time logging, we can use the concept of event listeners in Node.js. We will create a separate file called app.js where we will listen for events such as log messages and log events.

// app.js
const logger = require('./logger');

logger.on('log', (log) => {
  console.log(`New log: ${log}`);
});

logger.on('error', (error) => {
  console.error(`Error: ${error.message}`);
});

logger.debug('This is a debug message');
logger.error('This is an error message');

In the above code, the logger.on('log') event listener will trigger whenever a log message is being generated. Inside the event listener callback, we can perform any custom logic, such as displaying the log message in real-time.

Similarly, the logger.on('error') event listener will trigger when an error occurs during logging. Inside the event listener callback, we can handle the error accordingly.

Conclusion

In this blog post, we explored how to implement real-time logging using Log4js in a Node.js application. By leveraging the event listeners functionality in Node.js, we can easily track and display log messages as they occur.

Real-time logging can be invaluable for debugging and monitoring applications, allowing developers to quickly identify issues and resolve them promptly.

#logging #Nodejs