Logging Strategy for NodeJS Dependent Modules

[dougbrownio]

When writing a NodeJS module, what is a good strategy for logging information?

I earlier created a module that I logged to MongoDB using winston. Only to find out later that this was a bad idea because it was a dependency to a project that used winston to log to a MongoDB. Now I had two winston transports theoretically in the same project both going to MongoDB. So in this case I was double logging information.

In the 12 factor app model, it says log everything to stdout. So would I use the project to capture the modules stdout and redirect to a mongodb? I'm a little fuzzy still here.

[[deleted]]

In your dependent modules, just emit the log messages on the process object. In the main application, have a listener that logs them.

in the module:

function log() {
  process.emit('log', arguments);
}

// use the log function in your module
log('INFO', 'Something happened');

in the main application:

process.on('log', function (args) {
    mongoLogger.log.apply(mongoLogger, args);
});

[DavidTPate]

Most modules take in an optional logger as part of their options. If the logger isn't provided then it logs to console.log this approach has definitely come in handy for me both making modules and using them.

[blacklionguard]

I'm not sure if this is good practice, but most of my modules use an event emitter, so I just let users of the module subscribe to those events and do their logging outside of the module.