Logging on Node.js with winston

winston is very popular logger for Node.js, providing simple API to store and format the logs. It provides support for custom logging levels, streaming logs and custom transports to save the logs. Another useful feature is the ability to query the logs based on filters like duration and keywords.

In this post, we'll explore how winston can be used to log to the console as well as a file.

Setup

You can pick the Node.js application created in the post Request logging with morgan to follow this post.

Install dependencies

Add winston and winston-daily-rotate-file as dependencies.

yarn add winston winston-daily-rotate-file

Configure the logger

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

typescript

 1// src/helper/default.logger.ts
 2
 3import winston from 'winston';
 4import DailyRotateFile from 'winston-daily-rotate-file';
 5import { environment } from '../configuration/environment';
 6
 7export const logger = winston.createLogger({
 8  level: environment.logLevel,
 9  format: winston.format.simple(),
10  transports: [
11    new winston.transports.Console(),
12    new DailyRotateFile({
13      filename: environment.logFile,
14      dirname: environment.logDir,
15      datePattern: 'YYYY-MM-DD',
16      zippedArchive: true,
17      maxFiles: '14d',
18      maxSize: '20m'
19    })
20  ]
21});

Here, we've configured winston with two transports, Console and DailyRotateFile. DailyRotateFile will write the logs to logs/app.log file which'll be rotated every day or if it exceeds the size of 20 MB. The logs will be kept for up to 14 days in zip archives.

To use the logger, import it and call the logging methods (info, debug, etc).

typescript

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-winston

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