CentOS is stable as a rock. Fedora is edge and stable too (from my own experience). You will never fill the lack of packages or support or documentation if you will choose RHEL or RHEL based distros. https://webtatic.com/ Here you can read how to install and maintain latest versions of PHP, MySQL, NginX and other web related services on some RHEL based systems.

https://developer.mozilla.org/en-US/docs/Web/JavaScript - is the best description with examples and browser compatibility. http://jstherightway.org/ http://stackoverflow.com/ https://www.webcodegeeks.com/ http://www.codewars.com/?language=javascript