And if you are not authenticated, you are instead taken to a login page. Logging in then gives you the redirect and the upvote is registered.
But it'd be a quick performance win if it didn't do that when you were logged in with JavaScript enabled. The actual JavaScript part of this is actually already implemented -- that's why the page doesn't refresh when you upvote my comment -- so you'd just need one if-statement on the server side to send a blank response instead of a redirect.
Sure, 10 KB of download and the server CPU time needed to re-generate the listing page is probably pretty negligible, but multiply that by the number of votes casted on Hacker News every day and it starts to add up.
If someone loads this thread right now, the initial page load is 61KB (gzipped). If they read down the thread and vote on 30 comments while they're doing it, they transfer an additional 480KB (16KB/vote [1]). There's no reason that they should be receiving 8x more data by voting on a relatively low number of comments (~10% of the thread) than they did when loading the entire page originally. It also has to re-generate the page an extra 30 times unnecessarily - a repeatedly voting user becomes like a heavy multiplier to your traffic.
[1]: Also, I just noticed that the responses back from voting actually aren't the full page, they're truncated. It seems like maybe the response size is capped at 16KB gzipped? That implies that there's already some kind of special handling for the voting responses.
Taking data from 2.5 years ago[0], HN has ~300k daily uniques. Assuming 10% of that are users, each upvoting one story, that's 30k unnecessary page renders per day. That's ~2% of the total views (though the more expensive views - AFAIK when you're logged out, you get cached pages?), so on the one hand it's not much, but on the other hand the fix should be trivial and have minimal impact on code readability.
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