Honestly, I think process.js is not suitable for what you want, it was created to work with the new canvas element, and not with a web page.
Also, I think (honestly) I think that sucks. They handle processing using Regex, this is completely wrong; you cannot parse a programming language with Regex.
There is a javascript compiler compiler called JS / CC , it is very easy to use, just learn the grammar and you can make a simple programming language.
But if you want to make a complex language (for example, processing or php) yourself, get ready for nightmares.
PS: you need to know Javascript to implement a programming language in Javascript ...
user216441