auto scroll

[benjaminpreiss]

thread view should auto-scroll up on:

• switch to thread view
• new contents being inserted at top of thread view (if were scrolled to top before.)

Also switch to a scroll trigger based on scroll height diff and not element insertion.

[benjaminpreiss]

Some more thoughts:

• Watch body height change with resize observer. Don't debounce, as it triggers max. 60 times per second anyway (every 10 ms)
• Also watch window resizes (only shrinks!). As one resizes the window, we'd want to update the scroll position (e.g.). Debounce (not throttle).

Scroll to bottom on the following events:

• freshly navigated to chat view (no event necessary, no conflict if resize observer fires)
• new element gets added to chat view, and it's either mine or I was(!!) already scrolled to the bottom (resize observer event, no conflict with window resize)
• window resize, and I was already scrolled to the bottom (window resize event, no conflict with resize observer)

Event	Condition	Action
freshly navigated to chat view	true	scrollToBottom
resize observer event (on body element)	latest element is either mine or I was(!!) already scrolled to the bottom	scrollToBottom
window resize (debounced!)	I was already scrolled to the bottom	scrollToBottom
-	-	-
freshly navigated to thread view	true	scrollToTop (I think this is happening automatically)