Just thinking here. If you did not have SPA, couldn't you just I don't know log when they request those pages? Like, aren't those done with HTTP request anyway... So why the hell you need to do the logging on client side...
Then again that would be fun to send enough nice bogus log information... As clearly that is what they want.
This works as long as the user is navigating around inside your site - but it won't work if the user e.g. navigates to a different domain or closes the browser window.
If you specifically want to track when a user leaves a page, you will miss a lot of events this way.
Of course there is no way to perfectly, reliably capture 100% of the events. Even if browsers had a dedicated API for that, a user could simply kill the process or pull the plug.
However, you can make sure you capture the vast majority of events. Clicking on a link or closing a tab are much more likely events than killing the browser or leaving a tab open for weeks.
(On desktop at least, might be different for mobile. But even there, you might want to track how many pages just stay open forever - which would also require you to track close events.)
Then again that would be fun to send enough nice bogus log information... As clearly that is what they want.