What's a simple way to define multiple jQuery.Callbacks() prerequisites?
<p>What's the simplest way to define multiple jQuery.Callbacks() prerequisites?</p>

<pre><code>// simple pubsub example
var pubsub=(function() {
    var callbacksObj={};
    return function(id){
        if(!id) throw 'callbacks requires an id';
        return (callbacksObj[id] = callbacksObj[id] || $.Callbacks('unique memory'));
    };
})();
function fn1(){
    console.log('fn1');
};
function fn2(){
    console.log('fn2');
};
function fn3(){
    console.log('fn3');
};

// subscribing
pubsub('foo').add(fn1);
pubsub('bar').add(fn2);
pubsub('foo','bar').add(fn3); // adding a function with multiple dependencies

// publishing
pubsub('foo').fire() // should only log 'fn1';
pubsub('bar').fire() // should log both 'fn2' AND 'fn3' since both have fired
</code></pre>

<p>I can see wrapping each added function in another function that checks each id's fired() state, though this seems like a common enough scenario that perhaps there's a simpler way I'm missing.</p>
