@arction/eventer

Eventer

Simple and fast event emitter library. Subscription is based on a unique Token, which can be used to unsubscribe from the topic.

The Eventer is used in LightningChart^® JS charting library. https://www.arction.com/

Installation

npm install --save @arction/eventer

Documentation

Online documentation is available at arction.github.io/eventer

Getting started

import { Eventer } from '@arction/eventer'

const eventer = new Eventer()

// new topic is created, handler is added as the first subscriber to the topic
const token1 = eventer.on('topic1', () => console.log('I am called from topic1'))
// 'topic1' already exists, so new listener is simply added to existing collection of handlers
const token2 = eventer.on('topic1', () => console.log('I am also called from topic1'))
// new collection of handlers is created for the second topic
// the function is added to it
eventer.on('topic2', () => console.log('I am called from topic2'))

eventer.emit('topic1')
// calls two functions which listen to the event
//
// outputs:
//    I am called from topic1
//    I am also called from topic1

eventer.emit('topic2')
// calls single functions which listen to the event
//
// outputs:
//    I am called from topic2

// remove the second listener from the first topic by token 
eventer.off(token2)

eventer.emit('topic1')
// calls single functions which listen to the event
//
// outputs:
//    I am called from topic1

// remove all listeners from all topics
eventer.allOff()

eventer.emit('topic2')
// nothing happened, since all subscriptions were terminated

Subscribe to topic

Subscribing to a topic is easy.

eventer.on('topic', ()=>{ console.log('Topic handler') })

Multiple subscriptions to a single topic can exist.

eventer.on('topic', ()=>{ console.log('Topic handler') })
eventer.on('topic2', ()=>{ console.log('Topic 2 handler') })
eventer.on('topic3', ()=>{ console.log('Topic 3 handler') })

Unsubscribe from topic

You can unsubscribe from a single topic by using the Token returned by eventer when you subscribed to the topic.

const token = eventer.on('topic', ()=>{ console.log('Topic handler') })

eventer.off(token)

You can also unsubscibe all listeners from a topic.

eventer.topicOff('topic')

It is also possible to unsubscribe all topics and all listeners.

eventer.allOff()

Emiting events

Events can be emitted for a topic. The emit can contain 0 or more arguments that will be provided to the topic listeners.

eventer.emit('topic')

eventer.on('topic2', ( arg1, arg2 ) => console.log( arg1, arg2 ))

eventer.emit('topic2', 'Hello ', 'World')

Development instructions

The project is developed using TypeScript. Build system of the project heavily relies on Node.js. Dependencies are managed with npm, therefore, remember to run npm install before starting of anything else.

There are several npm scripts, which are used for development process:

Name	Command	Description
build	npm run build	run build system
test	npm test	run tests and watch
lint	npm run lint	run static analyzer and watch
docs	npm run docs	generate typedoc documentation
ci:test	npm run ci:test	run tests once
ci:lint	npm run ci:lint	run static analyzer once
ci:watch	npm run ci:watch	run CI circle and watch

Changelog

[1.0.2] - 2022-09-21

Changed

• Upgraded development dependencies

Fixed

• Fixed event listener being called immediately when a new listener was attached to topic during event emitting for same topic.
  • This could have easily resulted in an infinite loop being created as new listeners are added to be processed last in the listener order.