Really simple node-like event emitter

emitter.js

// Definition
function EventEmitter() {
  var handlers = {}

  this.on = function (event, cb) {
    if (!handlers[event]) {
      handlers[event] = []
    }
    handlers[event].push(cb)
  }

  this.emit = function (event) {
    if (!handlers[event]) { return }
    var args = Array.prototype.slice.call(arguments, 1)
      , self = this

    handles[event].forEach(function(handler) {
      handler.apply(self, args)
    })
  }
}

// Usage
var foo = new EventEmitter()

foo.on('hello', function(arg) {
  console.log("foo: hello: %s", arg)
})

foo.emit('hello', "world!")