Introduction

Simple logging module written in TypeScript.

Levels

There are 5 log levels:

const Logger = require("loggol")

Logger.Level.DEBUG
Logger.Level.INFO
Logger.Level.WARN
Logger.Level.ERROR
Logger.Level.OFF

Logging to the console

The following code creates a logger object that writes to stdout and stderr in the format [dd/mm/yyyy hh:mm:ss][LEVEL][TAG]: message]:

const Logger = require("loggol")

const logger = new Logger.Console({
	tag: "Logger1",
	level: Logger.Level.DEBUG,
	format: Logger.Format.standard
});

logger.debug("debug");
logger.info("info");
logger.warn("warn");
logger.error("error");

If you would like colours and your terminal supports it, replace Logger.Format.standard with Logger.Format.standardColoured

Logging to a file

The following code creates a logger object that writes to a file stream of your choice, in the same format as above

const fs = require("fs");
const Logger = require("loggol")

const logger = new Logger.File({
	tag: "Logger2",
	level: Logger.Level.DEBUG,
	format: Logger.Format.standard,
	file: fs.createWriteStream("output.log", {
		flags: "a",
		encoding: "utf-8"
	})
});

Chaining loggers

Often you could find yourself wanting to log the same data to two or more different output, you can do this by using the chain method of the Logger prototype

const Logger = require("loggol");

const logger1 = new Logger.Console(...);
const logger2 = new Logger.File(...);
const logger3 = new Logger.File(...);

logger1
	.chain(logger2)
	.chain(logger3)

logger1.info("hello!");
// logs to logger2 and logger3 as well

logger2.info("wow");
// logs to logger3, but not logger1 

Creating your own format

Format functions receive a LogData object:

type LogData = {
	date: Date;
	tag: string;
	level: number;
	items: any[]
};

Just to clarify, since the others are self explanatory, items is just an array of whatever the calling code wanted to log.

Your function should look something like this:

function myFormat({ date, tag, level, items }) {
	// create output here
	// return string
}

Then you can pass this function around to all your loggers that need to use it.

Creating your own Logger

If the included implemenations don't quite fit your needs you can always implement your own and keep the same public interface.

const Logger = require("loggol");

class OtherLogger extends Logger.Abstract {
	write(message) {
		// whatever needs to happen to log 'message'
	}
}

Logger factories

Sometimes you may not want to use a single logger with the same tag and level. A function that you can import everywhere a logger is needed is great for creating a bunch of similar logger objects.

For example, a lot of files I have only need Logger.Console and they should all have the same level and format, but a different tag.

const Logger = require("loggol");
const level = Logger.Level.INFO;
const format = Logger.Format.standardColoured;

function createLogger(tag) {
	return new Logger.Console({
		tag,
		level,
		format
	});
}

module.exports = createLogger;

You could also do something similar to return different types of Logger's