Usually you have a bundler/transpiler running on the host, with sandpack we moved that step to the browser so you can share a link with anyone and they instantly get a development friendly (JSX, TS, ...) project that works without having to install any tooling. It's also a lot faster than something like webpack as most of the bundling complexities are taken away as sandpack transpiles files on demand without the need for bundling as it also controls code execution. With nodebox we pushed this a bit further by also implementing most of the Node.js standard libraries.