Chen Bin posted some nice Elisp on how to make flyspell at little more useful when dealing with Web-mode buffers. The problem is that many tag elements fail the spell check and you get a lot of spurious misspelling warnings.
Chen’s code fixes this so that only appropriate parts of the HTML are checked. He also shows how to extend this to Javascipt as a way of pointing to ways of extending his methods to other modes. If you do a lot of work in Web-mode or you’re looking for a way of solving the same problem in some other mode, take a look at Chen’s code.