murmle

Logging shouldn't be overly complex. Logging libraries are huge, with all sorts of stuff to e.g. email logs or rotate logs etc. This goes against the UNIX philosophy - just write your logs to STDOUT and use another tool to do the other stuff, e.g. logrotate(8).

You have to look at STDOUT and STDERR anyway, otherwise you might miss stacktraces from catastrophes, so really all your logging should go there.

Also, wading through logs is tiring, so maybe they should just be JSON and you can use tooling to search them.

Usage

import Logger, { writePretty, writeJson } from 'murmle';

// write JSON if we're in production and
// pretty output (more human readable) if we're not
if (process.env.NODE_ENV === 'production') {
  Logger.default.on('log', writeJson);
} else {
  Logger.default.on('log', writePretty);
}

Logger.default.info('a thing happened');

With the pretty writer, this outputs:

✔ [2017-01-06 22:21:04] info a thing happened

And with the JSON writer:

{"level":30,"message":"test message","time":"2017-01-06T22:33:46.276Z"}

There is also a writeBunyan function to write Bunyan-compatible JSON output.

The log object

Every log object has a level and a time. Simple ones also have a message, and any other field can be included.

Log levels

Name	Numeric value	Description
trace	10	Very detailed logging, external libraries, etc.
debug	20	More detailed than info.
info	30	Detail on regular operation.
warn	40	A potential problem that should be looked at eventually.
error	50	An error affecting the current operation or request, which leaves the application functioning.
fatal	60	The whole application has borked.

The Logger class has a method for each of these levels, which have the following signatures:

• (message: string, ...args: any[]) - logs an object with message field set as specified, with optional util.format arguments

• (obj) - logs the specified object, adding the time and level fields automatically

There is also a log method, which is the same as above only it accepts a first argument of LogLevel to specify the log level dynamically.