An extremely light-weight logger for node.js

Install

$ npm install --save @viva-eng/logger

Basic Usage

import { Logger, ReadableFormat, StdoutOutput } from '@viva-eng/logger';

const logger = new Logger({
	format: ReadableFormat,
	output: new StdoutOutput(),
	colors: true,
	level: 'info'
});

logger.info('Hi there');

There are 6 logging methods: error, warn, info, verbose, debug, and silly.

Outputs

Any normal writable stream can be used as an output. It will receive messages to be logged. That's about all there is to say about that.

There are 2 outputs built in to the library. The StdoutOutput is just a thin wrapper around process.stdout. The other is the ClusterOutput which is designed to enable logging from workers in a clustered application. It works by passing the messages to be logged up to the master process using IPC, and the master process then logs the message to ensure that messages don't interlace with each other in unusual ways.

import { isMaster } from 'cluster';
import { Logger, ReadableFormat, StdoutOutput, ClusterOutput, ClusterOutputReceiver } from '@viva-eng/logger';

export let logger;

if (isMaster) {
	logger = new Logger({
		format: ReadableFormat,
		// Use whatever output you want here, this is where your logs will
		// end up for all workers and the master
		output: new StdoutOutput()
	});

	// Pass the logger into the receiver so it knows what to do with the messages
	const clusterOutputReceiver = new ClusterOutputReceiver(logger);
}

else {
	logger = new Logger({
		format: ReadableFormat,
		// This will forward all log messages up to the master
		output: new ClusterOutput()
	});
}

logger.info('Hi there! I work in all processes!');

Formats

A format is any object that implements the Format interface, which looks like this:

interface Format {
	format(level: string, message: string, meta?: object): string;
}

It takes in the message to be logged and formats it in whatever way you want, so long as the end result is a string.

There are two formats built in, the ReadableFormat which is a human-readable pretty print format (optionally with colors!) and the JsonFormat which outputs all your logs in JSON.