winston.rejections returns undefined

[Suren55]

Please tell us about your environment:

• winston version?
  • winston@3
• node -v outputs: 14.16.1
• Operating System? Windows
• Language? ES6

What is the problem?

winston.rejections is undefined when trying to call:

winston.rejections.handle( new winston.transports.File({ filename: 'rejections.log' }) );

What do you expect to happen instead?

I expect to be able to make the above mentioned call and log the error.

[DiniFarb]

Hello @Suren55

I think there is a mistake in the docs:

this should be the logger and not the winston itself.

Maybe you could do something like:

const { createLogger, transports, format } = require('winston');

const logger = createLogger({
    format: format.combine(
        format.timestamp({ format: 'YYYY-MM-DD HH:mm:ss:ms' }),
        format.printf(info => `${info.timestamp} ${info.level}: ${info.message}`)
    ),
    transports: [
        new transports.Console(),
    ]
});

logger.rejections.handle(
    new transports.File({ filename: 'rejections.log' })
);

logger.info("Start ...");

const myPromise = new Promise((resolve, reject) => {
    reject('Ouch');
});

myPromise.then(() => {
    console.log('Hello World');
});

[Suren55]

Hi @andreasvogt89. Thank you for the reply, however I am not sure that it's a mistake in the docs, because the same logic exists for winston.exceptions.handle() and it works just fine.

Also, thank you for the piece of code you provided, but I did not want to create a custom logger, I wanted to use the default one for now.

[DiniFarb]

Yes you are right, it does not work for the default logger.

The problem is that rejections which is the RejectionHandler object is not exposed to the winston.

If I try to use the alternativ way like below, it caught the UnhandledPromiseRejection but did not write it to the file.

const winston = require('winston');

winston.add(new winston.transports.File({
    filename: 'rejections.log',
    handleRejections: true
}));
    
winston.info('Starting. . . ');

const myPromise = new Promise((resolve, reject) => {
    reject('Ouch');
});

myPromise.then(() => {
    console.log('Hello World');
});

I think best way to solve would be to add rejections to the default property exposer in winston.js so the rejections can be used with winston (defaultLogger)

/**
 * Define getters / setters for appropriate properties of the default logger
 * which need to be exposed by winston.
 * @type {Logger}
 */
['exitOnError', 'rejections'].forEach(prop => {
  Object.defineProperty(winston, prop, {
    get() {
      return defaultLogger[prop];
    },
    set(val) {
      defaultLogger[prop] = val;
    }
  });
});