Winston - MaxListenersExceededWarning: Possible EventEmitter memory leak detected

Question

Got below error in winston when using file logging with winston-daily-rotate-file package, code works well with winston console logging,

  MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 error listeners added. Use emitter.setMaxListeners() to increase limit
        at _addListener (events.js:256:17)
        at DailyRotateFile.addListener (events.js:272:10)
        at DailyRotateFile.once (events.js:301:8)
        at asyncForEach (/home/ubuntumachine/Desktop/project/node_modules/winston/lib/winston/exception-handler.js:217:17)
        at /home/ubuntumachine/Desktop/project/node_modules/async/internal/withoutIndex.js:9:16
        at eachOfArrayLike (/home/ubuntumachine/Desktop/project/node_modules/async/eachOf.js:65:9)
        at exports.default (/home/ubuntumachine/Desktop/project/node_modules/async/eachOf.js:9:5)
        at eachLimit (/home/ubuntumachine/Desktop/project/node_modules/async/forEach.js:80:24)
        at ExceptionHandler._uncaughtException (/home/ubuntumachine/Desktop/project/node_modules/winston/lib/winston/exception-handler.js:203:5)
        at process.emit (events.js:198:13)
    (node:20805) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 finish listeners added. Use emitter.setMaxListeners() to increase limit
        at _addListener (events.js:256:17)
        at DailyRotateFile.addListener (events.js:272:10)
        at DailyRotateFile.once (events.js:301:8)
        at asyncForEach (/home/ubuntumachine/Desktop/project/node_modules/winston/lib/winston/exception-handler.js:216:17)
        at /home/ubuntumachine/Desktop/project/node_modules/async/internal/withoutIndex.js:9:16
        at eachOfArrayLike (/home/ubuntumachine/Desktop/project/node_modules/async/eachOf.js:65:9)
        at exports.default (/home/ubuntumachine/Desktop/project/node_modules/async/eachOf.js:9:5)
        at eachLimit (/home/ubuntumachine/Desktop/project/node_modules/async/forEach.js:80:24)
        at ExceptionHandler._uncaughtException (/home/ubuntumachine/Desktop/project/node_modules/winston/lib/winston/exception-handler.js:203:5)
        at process.emit (events.js:198:13)
    (node:20805) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 31 error listeners added. Use emitter.setMaxListeners() to increase limit
        at _addListener (events.js:256:17)
        at Console.addListener (events.js:272:10)
        at Console.once (events.js:301:8)
        at asyncForEach (/home/ubuntumachine/Desktop/project/node_modules/winston/lib/winston/exception-handler.js:217:17)
        at /home/ubuntumachine/Desktop/project/node_modules/async/internal/withoutIndex.js:9:16
        at eachOfArrayLike (/home/ubuntumachine/Desktop/project/node_modules/async/eachOf.js:65:9)
        at exports.default (/home/ubuntumachine/Desktop/project/node_modules/async/eachOf.js:9:5)
        at eachLimit (/home/ubuntumachine/Desktop/project/node_modules/async/forEach.js:80:24)
        at ExceptionHandler._uncaughtException (/home/ubuntumachine/Desktop/project/node_modules/winston/lib/winston/exception-handler.js:203:5)
        at process.emit (events.js:198:13)

Tried to set max listeners to infinity,

const EventEmitter = require('events');
const emitter = new EventEmitter();
emitter.setMaxListeners(Infinity);

still facing same issue.

Answer 1

I came accross a related case with the mentioned warning the headline, so just sharing insights from my investigation for others who might get into this thread:

• What is the reason this warning pops up? well, this comment in this relevant thread explains it well. In short: extensive usage of transports.
• How to disable the warning? I found few places (like this one) offering to update the max listener. They use process.setMaxListeners(0);, which is different from what used in the question.
• Should one disable the warning? I tend toward no (as explained in the first comment in this thread).
• Why clear() helped? well, I didn't read much about it, yet according to the documnation - It remove all transports.
• In what other cases this error might occur? - when one creates a lot of logger instances using transport. That was the case for me.

Answer 2

I had the same issue, it got fixed by calling winstonLoggerInstance.clear() when I was done with the logger. clear() clears all the transports.