MS Ajax Sys.require

Question

in ms ajax with below command we can load array of js files. and when those files are loaded callbackFn is called.

Sys.require(arrayOFFiles,callbackFn);

if any files out of arrayOfFiles is not downloaded because of some problem callbackFn is still invoked. So how can we detect like which files were downloaded successfully and which are not. testing for each namespace in arrayoFFiles wouldnt be a great idea.