The comma operator also seems forbidden. I guess there's never a need to use it in purely function code, but the code can still qualify as pure even allowing its use?
Currently, Leporello.js relies on my custom JavaScript parser, which, while functional, is not yet complete and exhibits some quirks. My plan is to replace it with a TypeScript parser, thereby providing full support for both JavaScript and TypeScript within Leporello.js. Additionally, I'm going to develop a VSCode extension, which will offer you all the features available in ts-server.