broadcast and receive global events in javascript

dispatcher.js

/*
    Dispatcher module
    by: wangyu (bigeyex@gmail.com)
    dispatch global event
    usage:
        - fire an event:
            dispatcher.dispatch('example.event.name', arg1, arg2...)
        - subscribe an event:
            dispatcher.subscribe('example.event.name', function(arg1, arg2...){});

*/
function Dispatcher(){
    this.eventList = {};
    var self = this;
    
    this.subscribe = function(eventName, eventHandler){
        if(self.eventList[eventName]===undefined){
            self.eventList[eventName] = [];
        }
        self.eventList[eventName].push(eventHandler);
    };
    
    this.dispatch = function(eventName){
        var args = Array.prototype.slice.call(arguments);
        args.shift();
        var eventList = self.eventList[eventName];
        if(eventList!==undefined){
            for(var i in eventList){
                eventList[i].apply(this, args);
            }
        }
    };
}
window.dispatcher = new Dispatcher();

hi, how can i unsubscribe ?