I think what Vishu means is that you overlay the JS file. To do so, take
the file
at/libs/dam/gui/coral/components/commons/fileupload/clientlibs/fileupload/js/fileupload.jsCopy
it to
/apps/dam/gui/coral/components/commons/fileupload/clientlibs/fileupload/js/fileupload.jsThen
make your modifications.When AEM fetches fileupload.js, it will first
look under /apps and if it does not find anything, then under /libs The
concept is explained here: Overlays