How can I use the ftp to host .js files

[Meishin]

You don’t include htdocs in your URL.

That is to say you will probably bump into this when connecting your website with Roblox:

Browser Security System - Features and Limitations

InfinityFree uses a security system on all free hosting accounts to ensure your website is accessed by real web browsers, not bots or automated scripts. While this protects your site from malicious traffic, it can affect certain types of access. How the security system works The system checks that visitors can execute JavaScript and accept cookies: features that all modern web browsers support. This verification happens automatically and most website visitors will never notice it. You may occa…