It would be nice if one can run node.js code inside Excel user-defined functions. Something like using js code like VBA. I googled for solutions but cannot find any. Is it possible to do this?
Yes, if you want to use packages from NPM. You could use webpack to combine all the stuff to one js file, it should work.
webpack as a static module bundler for modern JavaScript applications. When webpack processes your application, it internally builds a dependency graph which maps every module your project needs and generates one or more bundles. you could refers to this document.
You could also refer to a sample, Yeoman, the Yeoman generator creates a Node.js Office Add-in project. it use webpack combine all files into one js file.