If we ever make it around to a second piece of javascript on here, can I request that it be a collapse comment function? I promise i won't ask for anything else.
It also highlights new comments and collapses threads without new comments on repeat visits. HN now feels unusable without it in scenarios where I can't use a userscript :-/
Quality—don't want to make it too easy to ignore entire chunks of the conversation, and don't want to encourage adding chunks to the conversation that are worth ignoring.
If you want the state of your collapsed comments to be remembered between session you're adding a lot of data to the backend of HN. I can see not implementing it, because threads are short lived and rarely get more comments that can be reasonably browser or searched.
I don't see that collapsing comments would really add much value, especially if the state is to kept per user per comment in the backend.
If you don't care about state, I feel reasonably sure that you could Greasemonkey your way out of not having that feature.
Alternatively, I'd appreciate if comments had a link to their siblings and not just their parents. It wouldn't require any JavaScript, but would (for me) have the same utility.
I wrote this a while ago, which seems to work. I reused the vote arrow with 1/4-turn rotation, placed on the other side of the comment header line to avoid confusion.
I don't know about other browsers, but this works OK on Chrome.