It saves the generated/rendered html, but I have just added a `spa` mode, that will save the original HTML without modifications. This makes most simple web app work.

I have also updated the local server for fetching from origin missing resources. For example, a webapp may load some JS modules only when you click buttons or links, when that happens and the requested file is not on the zip, it will fetch it from origin and update the zip. So mostly you can back up an SPA by crawling it first and then using it for a bit for fetching the missing resources/modules.

Note I've recently released a tool that can find all chunks of a SPA that works for popular configurations (like webpack or ES modules):

https://github.com/zb3/getfrontend

Thanks for sharing!