logmitter

  

Logmitter is a universal logging utility which acts as event emitter. It's a lightweight open-source package for the server and browser (using module bundler), written with TypeScript. It's actively maintained, well tested and already used in production environments. The source code is available on GitHub where you can also find our issue tracker.

Installation

Run the command below to install the package.

$ npm install --save logmitter

Usage

Logger class is an event emitter which provides standard methods for triggering and listening to different logging events. This class should be used as a central logger instance of your application.

Listening and triggering events

We create a simple logger by creating a new instance of a Logger class. We can then emit and listen to different logging events.

import { Logger, LogEvent } from 'logmitter';

const logger = new Logger(namespace);

logger.on(LogEvent.INFO, function({ date, event, message, namespace }) {
  console.info(message);
});

logger.info('Hello world!');

Custom message format

We can easily change the message format by setting a custom message interface.

interface Message {
  code: number;
  message: any;
};

const logger = new Logger<Message>(namespace);

logger.warn({ code: 200, message: 'Hello world!' });

Namespaced logger

To distinguish between application parts, you can namespace the logger instance by creating a child instance which passes all events to the master instance.

const userLogger = logger.child('user');

API

Logger(namespace)

Main logger class.

Option	Type	Required	Default	Description
namespace	String	No	-	Logger namespace.

Logger.prototype.child(namespace): LoggerChild

Returns logger child instance.

Option	Type	Required	Default	Description
namespace	String	No	-	Logger namespace.

Logger.prototype.debug(message): Boolean

Triggers debug event.

Option	Type	Required	Default	Description
message	Message	Yes	-	Event message.

Logger.prototype.emit(event, message, namespace): Boolean

Triggers log event.

Option	Type	Required	Default	Description
event	String	Yes	-	Event name.
message	Message	Yes	-	Event message.
namespace	String	No	this	Logger namespace.

Logger.prototype.error(message): Boolean

Triggers error event.

Option	Type	Required	Default	Description
message	Message	Yes	-	Event message.

Logger.prototype.info(message): Boolean

Triggers info event.

Option	Type	Required	Default	Description
message	Message	Yes	-	Event message.

Logger.prototype.namespace: string

Returns logger namespace.

Logger.prototype.off(event, resolver): Logger

Removes attached event listener.

Option	Type	Required	Default	Description
event	String	Yes	-	Event name.
resolver	Function, Promise	No	-	Event resolver function. All event with the provided name are removed when the resolver is not provided.

Logger.prototype.on(event, resolver): Logger

Attaches a listener function to log event.

Option	Type	Required	Default	Description
event	String	Yes	-	Event name.
resolver	Function, Promise	Yes	-	Event resolver function.

Logger.prototype.once(event, resolver): Logger

Attaches a listener function to log the event and automatically removes it after the event is triggered.

Option	Type	Required	Default	Description
event	String	Yes	-	Event name.
resolver	Function, Promise	Yes	-	Event resolver function.

Logger.prototype.warn(message): Boolean

Triggers warn event.

Option	Type	Required	Default	Description
message	Message	Yes	-	Event message.

LoggerChild(parent, namespace)

Logger child class.

Option	Type	Required	Default	Description
parent	Logger	Yes	-	Parent logger class instance.
namespace	String	Yes	-	Logger namespace.

LoggerChild.prototype.child(namespace): LoggerChild

Returns logger child instance.

Option	Type	Required	Default	Description
namespace	String	No	-	Logger namespace.

LoggerChild.prototype.debug(message): Boolean

Triggers debug event.

Option	Type	Required	Default	Description
message	Message	Yes	-	Event message.

LoggerChild.prototype.error(message): Boolean

Triggers error event.

Option	Type	Required	Default	Description
message	Message	Yes	-	Event message.

LoggerChild.prototype.info(message): Boolean

Triggers info event.

Option	Type	Required	Default	Description
message	Message	Yes	-	Event message.

LoggerChild.prototype.namespace: string

Returns logger namespace.

LoggerChild.prototype.warn(message): Boolean

Triggers warn event.

Option	Type	Required	Default	Description
message	Message	Yes	-	Event message.

Available events

Event	Value	Description
LogEvent.ERROR	error	Error event.
LogEvent.WARN	warn	Warning event.
LogEvent.INFO	info	Info event.
LogEvent.DEBUG	debug	Debug event.

Contributing

See CONTRIBUTING.md for how to help out.

Licence

See LICENSE for details.