# Events

## Events

Events module is implementation of node [events](https://nodejs.org/api/events.html#events_events).

Module requires no configuration and usage is quite trivial:

```
import { Events } from 'node-mariner';

// Register the event listener
const PubSub = new Events();


// Register event
const sampleMessageListener = message => {
  console.log('You sent sample message', message)
}

PubSub.on('sample-message', sampleMessageListener)

// Check if listener is properly registered
console.log(PubSub.count()) // returns 1

// Emit the event
PubSub.emit('sample-message', 'this is dummy message')
// results in 'You sent sample message', 'this is a dummy message'

// Deregister the listener
PubSub.off('sample-message', sampleMessageListener);

// Check if listener is properly deregistered
console.log(PubSub.count()) // returns 0
```

## Methods

Events provide 4 methods, with familiar [publish-subscribe](https://addyosmani.com/blog/understanding-the-publishsubscribe-pattern-for-greater-javascript-scalability/) naming pattern:

| method | arguments                 | description                                                                 |
| ------ | ------------------------- | --------------------------------------------------------------------------- |
| on     | (`eventName`, `callback`) | register listener for provided `eventName`                                  |
| off    | (`eventName`, `callback`) | unregister listener for provided `eventName`                                |
| emit   | (`eventName`, `payload`)  | emit an event  for particular `eventName`                                   |
| count  | none                      | returns count`<integer>` of registered listeners to particular Event object |