In JS everything is exactly the same, a project structure with a bunch of folders and individual files. Can be divided into arbitrarily many parts and work infinitely large command. Next, enter in build tools automated build, usually Grunt
, etc. some companies have their own tools for Assembly. In addition, these tools can track changes in files and rebuild the project until you press Ctrl+S, so you can all have a great look in the browser in real time.
So, as you can see, in real development on JS almost never have to work with large files.