@sapphirejs/event

Event

A thin wrapper for Node's native events. Mostly to offer a few abstractions, a base class to be extended by event classes, and generally a tighter integration with Sapphire Framework. Other than that, it doesn't have any logic of its own and can be completely ignored if you don't like even such thin abstractions.

Usage

$ npm install --save @sapphirejs/event

As you'd expect, events can be listened with on and emmited with emit.

const { Event } = require('@sapphirejs/event')

const event = new Event()
event.on('some.event', () => {
  console.log('Yay, I was called')
})
event.emit('some.event')

More interesting though, are event classes as a way to organize and encapsulate event handlers.

class SendWelcomeEmail {
  listen(userId) {
    // send email to user with id=userId
  }
}

event.on('user.registered', new SendWelcomeEmail().listen)
event.emit('user.registered', 10)

An event can have multiple listeners:

event.on('user.registered', new SendWelcomeEmail().listen)
event.on('user.registered', new SendConfirmationSms().listen)

// or

event.on('user.registered', [
  new SendWelcomeEmail().listen,
  new SendConfirmationSms().listen
])


event.emit('user.registered')

BaseEvent

The BaseEvent class enforces the usage of the listen method and has the capabilities to be extended by the framework, like injecting a context object as argument. It is completely optional to use, but if you decide on it, this is how it's used:

const { Event, BaseEvent } = require('@sapphirejs/event')

class SendWelcomeEmail extends BaseEvent {
  listen(userId) {
    // send email to user with id=userId
  }
}

const event = new Event()
event.on('user.registered', new SendWelcomeEmail())
event.emit('user.registered', 7)

Notice how we don't pass the listen method on the event listener. It is automatically resolved when extending BaseEvent.

Event Names

Event names can be anything unique, so a string or constant comes to mind. However, if you think about it, class are also a very good way of having non-string event names. You can't misspell them, because the runtime or even your IDE will complain, so fewer bugs. And they're so easy to use:

class UserWasRegistered {}

event.on(UserWasRegistered, new SendWelcomeEmail())
event.on(UserWasRegistered, new SendConfirmationSms())

event.emit(UserWasRegistered)