Based on your requirements of getting all resources for a page that can be created in JavaScript, I'd use something that handles JavaScript well on a headless server: Node.js. That engine has the capabilities you need, and NPM means someone has already written what you seek (especially since Node is used for testing of JavaScript web apps). However, your alternative processor types means you'll have to figure out if you can compile it from source instead of using a Windows, or Mac OS binary.