event-kit

This is a simple library for implementing event subscription APIs.

Implementing Event Subscription APIs

const {Emitter} = require('event-kit')
 
class User {
  constructor() {
    this.emitter = new Emitter()
  }
 
  onDidChangeName(callback) {
    this.emitter.on('did-change-name', callback)
  }
 
  setName(name) {
    if (name !== this.name) {
      this.name = name
      this.emitter.emit('did-change-name', name)
    }
 
    return this.name
  }
 
  destroy() {
    this.emitter.dispose()
  }
}

In the example above, we implement ::onDidChangeName on the user object, which will register callbacks to be invoked whenever the user's name changes. To do so, we make use of an internal Emitter instance. We use ::on to subscribe the given callback in ::onDidChangeName, and ::emit in ::setName to notify subscribers. Finally, when the User instance is destroyed we call ::dispose on the emitter to unsubscribe all subscribers.

Consuming Event Subscription APIs

Emitter::on returns a Disposable instance, which has a ::dispose method. To unsubscribe, simply call dispose on the returned object.

const subscription = user.onDidChangeName((name) => console.log(`My name is ${name}`))
// Later, to unsubscribe...
subscription.dispose()

You can also use CompositeDisposable to combine disposable instances together.

const {CompositeDisposable} = require('event-kit')
 
const subscriptions = new CompositeDisposable()
subscriptions.add(user1.onDidChangeName((name) => console.log(`User 1: ${name}`))
subscriptions.add(user2.onDidChangeName((name) => console.log(`User 2: ${name}`))
 
// Later, to unsubscribe from *both*...
subscriptions.dispose()

Creating Your Own Disposables

Disposables are convenient ways to represent a resource you will no longer need at some point. You can instantiate a disposable with an action to take when no longer needed.

const {Disposable} = require('event-kit')
 
const disposable = new Disposable(() => this.destroyResource())