How to prevent your JavaScript code from being stolen, copied, and viewed?

There are two kinds of user: There is the large group who couldn't care less. No need to protect against them.

Then, there is the group who really wants to see how you did it. There is no way to protect against them. They have all the tools and the knowledge to circumvent any protection you could come up with. You could use obfuscation but that's going to cost you money and time, so in the end, you can only lose.

Create a great product plus offer good support and people will be willing to pay for it. Castle building didn't work well in the past (lot of effort and it took just a couple of stones to tear them down) and it surely doesn't work today.

If you're afraid that your ideas are going to be stolen, then look for a new job, because they will be and there's nothing you can do.

It's simply not possible.

For a visitor's browser to be able to execute the script, they have to be able to download it. Not matter what trickery you try to pull with JS, server permissions etc., at the end of the day they can always just wget http://example.com/yourcoolscript.js. And even if they can't (e.g. you require "secret" headers for that request) that would likely inhibit the behaviour of most browsers, while not stopping a determined person from looking anyway.

Fundamentally, because JS is executed client-side, the client must have access to the "original" JS file.

One minor thing you can do is obfuscation, which can help a little bit. But since JS is interpreted, it's also its own deobfuscator - see one of my earlier answers for an example.

Basically - "if you build it, they will look". :-)