How can I upload and host a JS file on my NodeJS + React app?

[mak7kdnchk]

I tried to add scriptTag to my NodeJS + React app and I don't know how to upload my JS file to  https://my-app/foldername/scriptTag.js . I can't find any information on shopify website and google and in YouTube videos people already have this file uploaded. Could someone please guide me how to do this? I spent a lot of hours trying to find how to do this trick.