Simple JavaScript Pub/Sub object

gistfile1.js

var PubSub = {
    subscribe: function(ev, callback) {
        var calls = this._callbacks || (this._callbacks = {});

        (this._callbacks[ev] || (this._callbacks[ev] = [])).push(callback);
        return this;
    },
    publish: function() {
        var args = Array.prototype.slice.call(arguments, 0);

        var ev = args.shift();

        var list, calls, i, l;
        if(!(calls = this._callbacks)) return this;
        if(!(list = this._callbacks[ev])) return this;

        for(i = 0, l = list.length; i < l; i++) {
            list[i].apply(this,args);
        }
        return this;
    }
};