https://yeacreate.com/en/support-download/ntablet/ntablet-webos-firmwares.html
https://yeacreate.com/en/support-video/ntablet/ntablet-download-firmwares-in-windows.html
https://yeacreate.com/en/support-video/ntablet/ntablet-download-firmwares.html
And of course, you can customize your owned WebOS firmware for adding NodeJs/Python and etc...
If you using PHP and HTML5, you can you our offical firmware dedicatedly. Just put your codes into /home/ , and modify /etc/init.d/S91chromium (the path), that's would works.
If you wanna to use other languages, eg: NodeJS , Python, Perl and etc... You need to customize your owned WebOS via rootfs source code.Here is a tutorial link about compile setup compile environment:
https://yeacreate.com/en/support-video/ntablet/ntablet-setup-compile-environment.html
https://yeacreate.com/en/support-video/ntablet/ntablet-compile-kernel.html
https://yeacreate.com/en/support-video/ntablet/ntablet-compile-uboot.html