Javascript minimalist EventEmitter.

emitter.js

/**
 * `Emitter` constructor.
 */

var Emitter = module.exports = function Emitter() {
  this.callbacks = {};
};


/**
 * `Emitter` prototype.
 */

Emitter.prototype = {

  callback: function callback(event, cb, once) {
    (this.callbacks[event] = this.callbacks[event] || []).push([cb, !!once]);
    return this;
  },

  on: function on(event, callback) {
    return this.callback(event, callback, false);
  },

  once: function once(event, callback) {
    return this.callback(event, callback, true);
  },

  emit: function emit(event) {
    var args = Array.prototype.slice.call(arguments, 1);
    var newCallbacks = [];
    var ok = true;
    (tthis.callbacks[event] || []).forEach(function (item) {
      ok = ok && item[0].apply(undefined, args) !== false;
      item[1] || newCallbacks.push(item);
    });
    this.callbacks[event] = newCallbacks;
    return ok;
  }

};