I just found that when I do the same (definitely failing) call twice I get different results (and both are wrong as stated above):

CODE: Y.use('no-such-module', function (Y, result) {console.dir(result);})

RESULT 1: {data:["no-such-module"], msg:"success", success:true}
RESULT 2: {success:true}

One more update:

When I force the loader to try to load a module (by specifying a group and a pattern for it, and using a module name matching that pattern, so that the loader cannot decide if it's a valid module without trying to load it from the server) I get a (correct) error (success:false) in the response.

However, when I perform the call a second time I also get {success:true}, so it seems if there is a cache hit one always gets the same response.

'no-such-module' is a dev-time problem. Use the -debug version of the seed file during development and the console log will let you know you have a problem. Missing modules are currently messaged even when you use the -min file. Success is reported because these mistakes are normally typos, and YUI will attach what it can and try to continue -- I'll look at this part.

Regarding the error response you saw with pattern matched modules, you must be using firefox -- other browsers will report success even though there was a 404 error, or they will just hang until a timeout if defined. This is a general problem with script loading that I'm in the process of making easier to deal with.

> 'no-such-module' is a dev-time problem

I beg to differ - slightly :-) You're thinking of "closed" apps.

I have generic application code which depending on the URL of the link clicked loads a module with the appropriate name. If the link is /items/12 it loads "mysite-items", etc. So on the one hand yes, that COULD be considered dev. issue - but not if I don't control everything, all modules, all links and all pages. I would like to be able to live with an error introduced by one of many people or entities, for which no one would be personally responsible, it just happens that there's a link that SHOULD lead to loading the appropriate module, but there is no module. You guys make sure everything in YUI is sooo generic, modular, ready for distributed modular apps - living with fallability is one aspect.

Background: I have written (based on Dav Glass's work) a site that works with or without Javascript, all rendering is done on the server by node.js if necessary. Also, if there IS Javascript, I don't let the browser change the page - only the homepage is loaded and ALL links are intercepted, a URL which normally is /items/12 is translated to /#/items/12, so that my client side app keeps the original real URL (path) in the hash and history and bookmarks work. For any clicks on links that client side code loads a module "mysite-firstPartOfLink" (example as above) and let's it render into the content container of the page. It works! But I don't see how I can check in advance that every link will always have the appropriate module. Or, better, why I even should. Sure it's an error, but with the same argument you could say 404/Not Found pages are unnecessary because they should never happen. What if a user enters a link manually and mistypes it? What if a bookmarked link is no longer valid and now leads to the attempt to load a module that no longer exists? Anyway, this way the website's CSS and JS are loaded *and parsed* by the browser only ONCE in addition to all the other niceties of having the same code on client and server and of having it work with or without client-side JS. It works! Okay, that's not quite a necessary part of the bug report, just some background.

Fixes #2529742 - Better messaging in status object of use callback
View Commit: 75aad08cf19d9c79452baef05e450d79e3a0c847

Shipped in 3.6.0. Marking closed/fixed.