eventemitter(pure).js

/* Polyfill EventEmitter. */
var EventEmitter = function () {
    this.events = {};
};
 
EventEmitter.prototype.on = function (event, listener) {
    if (typeof this.events[event] !== 'object') {
        this.events[event] = [];
    }
 
    this.events[event].push(listener);
};
 
EventEmitter.prototype.removeListener = function (event, listener) {
    var idx;
 
    if (typeof this.events[event] === 'object') {
        idx = indexOf(this.events[event], listener);
 
        if (idx > -1) {
            this.events[event].splice(idx, 1);
        }
    }
};
 
EventEmitter.prototype.emit = function (event) {
    var i, listeners, length, args = [].slice.call(arguments, 1);
 
    if (typeof this.events[event] === 'object') {
        listeners = this.events[event].slice();
        length = listeners.length;
 
        for (i = 0; i < length; i++) {
            listeners[i].apply(this, args);
        }
    }
};
 
EventEmitter.prototype.once = function (event, listener) {
    this.on(event, function g () {
        this.removeListener(event, g);
        listener.apply(this, arguments);
    });
};