Formatting example

[tvld]

It took me long time to figure out some simple formatting. The examples I found with a formatter function, simply did not work for me. Finally I got this working:

  logger.add(new winston.transports.File({
    level: 'info', // Log this level and all higher priorities
    filename: 'myfile.log',
    format: winston.format.combine(
      winston.format(options => {
        return {
          'level': options.level,
          'message': options.message,
          'my_own_nr': 12345,
          'nice_text': 'hello there'
        }
      })(),
      winston.format.timestamp(),
      winston.format.json()
    )
  }))

Maybe good to add to documentation?

[xiulunlin]

+1
Don't know how to configure

[DABH]

Thanks! Could you clarify what this does that none of the examples in the readme or examples folder https://github.com/winstonjs/winston/tree/master/examples do? Just so we know how to call this snippet if we add it to the examples...

[tvld]

Good point. The search and retrieve for examples is often the hardest part ...
I suppose we could call it some kind of "simple direct json formatting" ?

[fourpastmidnight]

I also had trouble understanding how the formatters work. I set up this codesandbox.

What I've learned is that a format specified when creating the logger sets up a "global" or "base" format. In my case, I tend to use format.timestamp({ format: 'YYYY-MM-DD HH:mm:ss.SSSZZ' }). Then, in a transport, you can specify another format. That format can be composed via format.combine(formatters: Format[]). And at runtime, the logger format that was specified is then "combined" with the transport format(s) to obtain the resulting log entry format.

Note that some "formats" simply "mutate" properties of the log entry, such as the level, or the message, while others actually specify an output format, e.g. format.json(). You must have, at most, one "output format". (I actually don't know what happens if you have more than one--but I don't think you'll get the expected results, given what I've learned about Winston.) Be aware that format.combine creates a "pipeline" of formatters (or, as I like to call them, mutators). They will be applied in the order in which they appear in the array. So, if you specify an "output format" first, then later "mutating formatters" may not work.

Also, be aware if you are using multiple transports. I've come across what appears to be a nasty bug in Winston, where any transports after the first transport DO NOT get all the metadata that may be present on the info object: #1933.

[fourpastmidnight]

There is a comment on #1430 which resolves the issue with info "losing data" between transports.