The Neos Project follows the PSR-1 and PSR-2 standards for PHP code which are widely known and supported by code editors. We use https://styleci.io/ to check every incoming pull request for compliance to these standards. If you need to reformat code to PSR-2 you can use the php-cs-fixer to automate the process.
JavaScript styleguide TBD
We are preparing a refactoring of the JavaScript and will adjust the style at that point. This means any currently available styleguide for JavaScript that we followed in the past will be superseeded then.