Every time you collapse a thread, that's saved on the server. Then, if you return to the page, it will render those threads collapsed. So that's a decent amount of state.

I disagree. It’s Boolean and flat (there is neither sequential nor nested logic around the state). It does recurse for each sub thread, but only in the case where there is no state. There’s also no business logic built around it, only display logic. It also is updated from exactly one location in the application.

That said, it’s a very simple and effective design. It’s an excellent program. But it’s not a fair comparison against other applications which, for one reason or another, need significantly more advanced state.

Any time you vote a comment, that's state as well.