The short answer is that it can (usually) archive SPAs sucessfully. The long answer is that the wget archive method will download the JS, and in theory it should execute in the archived version just like it does on the normal site, but in practice it doesn't always work 100%. Luckily that's why ArchiveBox also saves a Chrome-rendered version of the page as a PDF, Screenshot, and DOM dump, so you should be able to archive most javascript-heavy content without too many problems.