djalbat 1525 days ago. https://github.com/djalbat/yapp In fact the improvements largely came from streamlining the BNF, which is now workable: https://github.com/djalbat/yapp/blob/master/es6/parser/javascript.js The readme file has been improved, too. Contributions are very welcome, not just for the JavaScript grammar but for any of the supported languages or indeed new plugins.