Why error logs appears in warning logs file - Node.Js & Winston

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In my Node.js REST API I am using Winston Logging to print the errors and info logs in a separated files. This is my Winston setup:

const { createLogger, format, transports } = require("winston");
const { timestamp, printf, errors } = format;

const logFormat = printf(({ level, message, timestamp, stack }) => {
  return `${timestamp} ${level}: ${stack || message}`;
});

const logger = createLogger({
  transports: [
    //new transports.Console(),
    new transports.File({
      level: "info",
      filename: "logsWarnings.log",
    }),
    new transports.File({
      level: "error",
      filename: "logsErrors.log",
    }),
  ],
  format: format.combine(
    timestamp({ format: "YYYY-MM-DD HH:mm:ss" }),
    format.json(),
    format.prettyPrint(),
    errors({ stack: true })
    //logFormat
  ),
  statusLevels: true,
});

module.exports = logger;

This is an example of one of my requests (info log is for req details):

deleteUser: (req, res) => {
    logger.info("This is an info log");
    mySqlConnection.query(
      "DELETE FROM Users WHERE user_id=?",
      req.params.userid,
      (err, rows) => {
        try {
          if (rows.affectedRows >= 1) {
            res.send("user deleted successfully");
          } else {
            res.status(500).send("Can't delete row");
          }
        } catch (err) {
          logger.error("this is error", { err });
        }
      }
    );
  },

I have a problem that error logs appears both in the error logs file and in the warning logs file. How can I fix it?

winston node.js error-handling
1 Answers

What is going on?

As mentioned in the documentation

Logging levels in winston conform to the severity ordering specified by RFC5424: severity of all levels is assumed to be numerically ascending from most important to least important.

const levels = { error: 0, warn: 1, info: 2, http: 3, verbose: 4, debug: 5, silly: 6 };

and

winston allows you to define a level property on each transport which specifies the maximum level of messages that a transport should log.

What that means? For example:

You used "info" level for logsWarnings.log file. it means that you are going to log itself and more important levels into the file (info, warn and error).

For logsErrors.log file you used "error" level. That means it will only log the error level logs because "error" has the highest importance.

That is why you are getting both in your logsWarnings.log file.

Solution:

You can separate logger like:

...
const formatConf = format.combine(
  timestamp({ format: "YYYY-MM-DD HH:mm:ss" }),
  format.json(),
  format.prettyPrint(),
  errors({ stack: true })
  //logFormat
);

const infoLogger = createLogger({
  transports: [
    //new transports.Console(),
    new transports.File({
      level: "info",
      filename: "./logs/logsWarnings.log",
    }),
  ],
  format: formatConf,
  statusLevels: true,
});

const errLogger = createLogger({
  transports: [
    new transports.File({
      level: "error",
      filename: "./logs/logsErrors.log",
    }),
  ],
  format: formatConf,
  statusLevels: true,
});
...

And use like:

errLogger.error("this is error", { err });
// or
infoLogger.info("This is an info log");

For more customization, please see the documentation.

user_115864870
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