(function($, exports) {
    exports.cache = {};
    exports.getAjaxData = function(url) {
        return cache[url] || $.get(url);
    };
})(jQuery, window);

$when(getAjaxData(‘foo.html’)).then(function(response) {
    //do something with data
cache['foo.html'] = response;
});

if your function returns a promise, you can do this:

var foo = doSomething();
foo.done(function(){
  // it’s done
});

but if, for some reason, the doSomething function changes so that it no longer returns a promise, but now returns a plain javascript object or a string or something, this code will break because there won’t be a “done” method on the returned object.

by using $.when(foo).then(function(){…}) instead, we don’t care what the return type is. it can be a promise, in which case the callback will fire when the promise resolves. or, it can be a plain old object or a string or anything else, in which case the callback will fire immediately.

Am I right? Thanks for another great post! 

I had to write something fairly similar and for what it’s worth here it is 
http://jsfiddle.net/bqC6U/3/My single page app makes an ajax call immediately after a page refresh to load the data. I have routed js modules that are dependent on this data waiting to render the backbone views. I didn’t want to trigger an event like “dataLoaded” in case the event was subscribed to after it had already fired. Any feedback (negative I assume) on my jsfiddle would be appreciated. I expect this problem has been solved before much more elegantly many years ago but my code is at least robust. Or is it?