The newer versions of emacs include JavaScript and other user modes useful for modern app development:

$ git clone git://git.savannah.gnu.org/emacs.git
$ sudo yum groupinstall "Development Tools"
$ wget ftp://ftp.gnu.org/gnu/autoconf/autoconf-2.68.tar.bz2
$ tar jxvf autoconf-2.68.tar.bz2
$ cd autoconf-2.68
$ ./configure; make; sudo make install
$ sudo yum install texinfo libXpm-devel giflib-devel libtiff-devel libotf-devel  
$ cd ../emacs
$ make bootstrap; sudo make install

This process can take upwards of 20-30 minutes.

With the git repo state as of 24 March 2015:

$ emacs --version
GNU Emacs 25.0.50.1
Copyright (C) 2015 Free Software Foundation, Inc.
GNU Emacs comes with ABSOLUTELY NO WARRANTY.
You may redistribute copies of GNU Emacs
under the terms of the GNU General Public License.
For more information about these matters, see the file named COPYING.

Via: http://haulynjason.net/weblog/?p=1592