Logging on Node.js with log4js-node

console.log has been a prevalent anti-pattern inherited by Node.js developers from years of printing to the console on a browser. While this is useful for quick debugging, it doesn't sit well with server-side design; it's hard to turn it off selectively, add log levels to it or redirect the logs to a file or database. Some good alternatives to the console.log are winston and log4js-node.

In this post, we'll explore the uses of log4js-node to print the logs on the console as well as a file.

Install dependencies for log4js-node

Add the required dependencies with the following command.

yarn add log4js

Add configurations for the logs

Add the following environment variables (through dotenv or environment variables of your system); they configure the default logging level of log4js-node and the name of the log file.

1LOG_LEVEL=info
2LOG_FILE=app.log

Read these configurations in src/configuration/environment.ts.

 1// src/configuration/environment.ts
 2
 3export const environment = {
 4  nodeEnv: process.env.ENV || process.env.NODE_ENV,
 5  logDir: process.env.LOG_DIR || 'logs',
 6  logLevel: process.env.LOG_LEVEL || 'info',
 7  logFile: process.env.LOG_FILE || 'app.log',
 8
 9  // Other environment variables
10}

Define appenders for log4js-node

Create a file src/helper/default.logger.ts and add the following code.

 1// src/helper/default.logger.ts
 2
 3import { configure, getLogger } from 'log4js';
 4import { environment } from '../configuration/environment';
 5
 6// appenders
 7configure({
 8  appenders: {
 9    console: { type: 'stdout', layout: { type: 'colored' } },
10    dateFile: {
11      type: 'dateFile',
12      filename: `${environment.logDir}/${environment.logFile}`,
13      layout: { type: 'basic' },
14      compress: true,
15      daysToKeep: 14,
16      keepFileExt: true
17    }
18  },
19  categories: {
20    default: { appenders: ['console', 'dateFile'], level: environment.logLevel }
21  }
22});
23
24// fetch logger and export
25export const logger = getLogger();

Here, we've created a console appender, and a rotating file appender that rotates the file logs/app.log in a zip archive everyday.

Use this logger as follows.

1// import the logger
2import { logger } from './helper/default.logger';
3
4// other configurations and initializations 
5
6// server
7app.listen(port, () => logger.info(`Server started at http://localhost:${port}`));

Start the application; you should see app.log in logs directory and the same logs printed on the console.

References

Source code — logging-with-log4js-node

Related

• log4js-node docs