Do you know a way to protect the JS code and make it visible only if requested by the remote?

Question

Theoretically JS runs in the browser, then after the first download can be easily copied and made to run directly from the local, without going through the remote server. Because I need to sell an application * js (pay-as-you-use) I need to check each request and make it available ONLY if required by that particular site and, of course, only if he paid.

Answer 1

It doesn't work. As soon as someone downloaded a copy of the JavaScript file, he or she can always save a copy of it and even redistribute it.

Thus you cannot protect the JavaScript itself - but assuming you rely on some client-server interaction (i.e. AJAX), the server would not respond to requests coming from non-authorized sources, thus rendering the client-side worthless.

If you need to protect your business logic, don't put it into JavaScript. Alternatively, sue everybody who uses your scripts without having obtained a license (not sure if this is practical, though ...).