@jalik/logger

Logger

A flexible logger to log messages to anything you want (console, file, database...), there's nothing more to say about it.

Introduction

Logging is an important part of an application lifecycle, from development to production, we always need to log messages for debugging or tracing errors and warnings.

This library is tested with unit tests.

Creating a logger

The first thing to do is to create a logger, it's deadly simple.

import Logger from "@jalik/logger";

const Logger = new Logger({
  // Activate the logger
  active: true,
  // Display message of given types in the console
  console: {
    debug: true,
    error: true,
    info: true,
    other: true,
    warning: true
  },
  // Display context in the console
  displayContext: false,
  // Display logger name in the console
  displayMessage: false,
  // Give a name to this logger
  name: 'main'
});

Note that options are available on each Logger instance via Logger.options.

Logging types

As you can imagine, there are different types of logging, this is useful to distinguish messages, so below are these types :

• debug : only used for debugging
• error : only used for errors and exceptions
• info : only used to display informative messages
• warning : only used to display warnings

You can access predefined logging types by importing them in your code.

import Types from "@jalik/logger/dist/types";

Types.debug;
Types.error;
Types.info;
Types.warning;

Logging messages

When you log a message, you can also provide an optional context as extra information, you have a dedicated method for each type of logging.

import Logger from "@jalik/logger";

const Logger = new Logger();

// Logs a debug message
Logger.debug("user json", {name: "karl"});

// Logs an error message
Logger.error("Forbidden", {error: new Error("forbidden")});
Logger.error(new Error("forbidden"));

// Logs an info message
Logger.info("Application started", {date: new Date()});

// Logs a warning message
Logger.warn("Disk usage is above 90%", {diskUsage: 92.6});

// Logs a custom type message
Logger.log("Plop", "custom-type");

Activating or deactivating a logger

By default a logger is activated, but you can deactivate it anytime you want by using the setActive(Boolean) method.

import Logger from "@jalik/logger";

const Logger = new Logger();

// Activate logger on production environment only
Logger.setActive(process.env.NODE_ENV === "PRODUCTION");

// And to check if the logger is active
Logger.isActive();

Listening events

The logger is flexible enough in the way that you can execute callbacks when an event occurs (debug, error, info, warning), so you could save logs to a database, a file or whatever you want.

import Types from "@jalik/logger/dist/types";
import Logger from "@jalik/logger";

const Logger = new Logger();

// With this event listener, you can do something when an error happens
Logger.on(Types.error, (message, context) => {
    // do whatever you want here...
    // save error to database, send an email...
});

// This will trigger the listener defined above
Logger.error("Cannot contact DNS server", {ipAddress: "8.8.8.8"});

Changelog

History of releases is in the changelog.

License

The code is released under the MIT License.

If you find this lib useful and would like to support my work, donations are welcome :)

Changelog

v1.0.4 (2018-04-02)

• Adds constructor option displayName: Boolean
• Adds constructor option name: String
• Adds method Logger.getName()