I would just like to note that while it may be "silly" or "useless" to insert licenses into minified JavaScript, it is nonetheless *legally required* to do so, regardless of the technical aspect of it.
My 2 points - during my own research about free licenses, I've decided that for JS, a good license is MPL 2.0: http://www.mozilla.org/MPL/2.0/
Its advantages are: 1) It's "strong file-level copyleft". "File-level" is good for JS, because it eliminates any problems of deciding whether a *.js file is or is not a part of a derivative work, and any problems of using together with differently licensed JS. 2) It's explicitly compatible with GPLv2+, LGPLv2.1+ or AGPLv3+. Incompatibility problem of MPL 1.1 caused triple licensing of Firefox (GPL/LGPL/MPL). 3) It does not require you to include long notices into every file. You only "must inform recipients that the Source Code Form of the Covered Software is governed by the terms of this License, and how they can obtain a copy of this License". You may even not include any notice in files themselves provided that you include it in some place "where a recipient would be likely to look for such a notice".
Also, what I've understood also was that CC-BY-SA is not good for source code at all, at least because it's incompatible with GPL. So CC-BY-SA licensed JS may be a problem.