Tiny event dispatcher using jQuery

tinypub.js

(function(exports, name, $){
    var GPub = function(){};
    GPub.observable = function(src){
        var _o = $({}), _l = {}, obj = src || {};
        var _d = function(e){ (e in _l) && (_l[e] -= 1); };
        var _a = function(e){ (e in _l) || (_l[e] = 0); _l[e] += 1; };
 
        obj.on    = function() { _o.on.apply(_o, arguments);  _a(arguments[0]); return this;};
        obj.off   = function() { _o.off.apply(_o, arguments); _d(arguments[0]); return this;};
        obj.emit  = function() { _o.trigger.apply(_o, arguments); return this;};
        obj.once  = function() { _o.one.apply(_o, arguments);     return this; };
        obj.emits = function(e){ return (e in _l && _l[e] > 0);};
 
        return obj;
    };

    GPub.bindable = function(src, set, get, bind){
        if(!('on' in src) || !('emit' in src)) this.observable(src);
        var _set = src[set], _get = src[get];
        var method = (function(key, value){
            var old = _get.call(this, key);
            var out = _set.call(this, key, value);
            if(this.emits('change')) this.emit('change', {old:old, value:value});
            if(this.emits('change:'+key)) this.emit('change:'+key, {old:old, value:value});
            return out;
        });
        if(bind) method.bind(src);
        src[set] = method;
 
        return src;
    };

    GPub.delegable = function(src, events){
        var event, e;
        // var _binder = function(handler){reutrn }
        for(e in events){
            event = events[e];
            src['on'+event] = (function(handler){
                this.on(event, handler);
            }).bind(src);
        } 
    };

    exports[name] = GPub;

})(this, 'GPub', jQuery);

//Create model
var M = function(){this.data={}};

M.prototype.set = function(key, value){ this.data[key] = value; return this;};
M.prototype.get = function(key,def){ return this.data[key] || def; };

//GPub will make M observable and bindable
GPub.bindable(M.prototype, 'set', 'get');

var m = new M();

m.set('test', 23).on('change', function(e, p){
    console.log('change: old %s new %s', p.old, p.value);
}).on('change:test', function(e, p){
    console.log('change.test: old %s new %s', p.old, p.value);
}).set('test',44);