After building and uploading, pushing an API to the web I can tell you that back end JS is really called server.js and its not the same although it is a bit similar. Here is an article they may help you with your question. Good luck
The scripting API consists of a load of functions related to things you would do in a browser, eg find an HTML element or listen for a button click or add some CSS styling.
Yes: are you doing something that only makes sense inside a browser?
So there are two things there that are built in to a browser:
Node doesn’t have anything to do with browsers (anything related to browsers makes no sense if you want to write programs that have nothing to do with browsers).
What it does instead is provide an API for operating system functionality. So stuff like dealing with files or handling network connections.
Browsers do not have access to your local filesystem, for extremely sensible security reasons. So you can’t really do that.