Inspired by Backbone, crafted in ES6.

This library currently houses only a minimalist event emitter implementation.

The EventEmitter class is built to have an API similar too, but smaller than, that of Node.js.

import {EventEmitter} from 'vertebrate';

let emitter = new EventEmitter();

emitter.emit(name, ...args);

Triggers all handlers registered for an event name to be called with args.

emitter.on(name, handler);

// or

emitter.addListener(name, handler);

Registers a handler function against the given name. The name can be anything (including objects etc.) except undefined. When an event is registered, it triggers the 'newListener' event, with the name and the handler function registered.

One important difference when compared with the Node EventEmitter is that a name-handler pair can only be registered once, since internally this implementation uses an ES6 Set. If you try to add the same event handler twice for the same event name, it'll ignore the second.

emitter.removeListener(name, handler);

Removes a previously registered handler, and emits the removeListener event with the name and the handler.

emitter.removeAllListeners(name);

Removes all event handlers for the given name registered with the emitter. Emits the removeListener event for each removed handler (see above).

emitter.removeAllListeners();

Remove all event handlers for all names registered with the emitter. Emits the removeListener event for each removed handler (see above).

The most obvious thing that this implementation of EventEmitter is missing is a once method. This is deliberate. Writing an event that fires once is easy:

var emitter = new EventEmitter();

function logOnce(message) {
  console.log(message);
  emitter.removeListener('message', logOnce);
}

emitter.on('message', logOnce);

emitter.emit('message', 'hello, world'); // logs
emitter.emit('message', 'oh noes! :(');  // does't log

and doing so keeps the implementation of removeListener and the storage of events simple.