IMO copyright law is probably the most effective way to prevent your media being stolen. In most countries your work automatically copyrighted and nobody else is allowed to use it without your permission by default. Technical measures can ward off non-developers, but anyone who knows what they are doing will probably be able to circumvent the various tricks you can use to check the domain etc.
Also make sure you tick 'minify script' on export - that does some pretty sophisticated obfuscation of the code with Google Closure Compiler, and will make it far more difficult to reverse engineer. To date I'm not aware of any cases of minified projects being reverse engineered. That makes it a lot less useful to try to rip off games - you either have to basically copy the thing wholesale, which is obvious, or take some of the assets and you're back to square one designing the game logic, which is often enough work that you may as well make your own assets while you're at it too.