When you do a push, git only takes the changes that you have committed.
Remember when you do a git status it shows you the files you changed since the last push?
Once you commit those changes and do a push they are the only files that get pushed so you don’t have to worry about thinking that the entire master gets pushed because in reality it does not.
How to push a single file:
git commit yourfile.js
git status
git push origin master