When updates land

Solid collects the writes made in one event and applies them together when your code finishes. That keeps the page from showing half an update, but it means a read right after a write still sees the old value:

setItems((list) => [...list, item]);
items().length; // still the old length

Usually the fix is to stop reading there at all: a summary computed from items is a derived value, always correct.

When imperative code really needs the update applied, for example to scroll to a row that was just added, call flush(). It applies pending writes and updates the DOM before the next line runs:

setItems((list) => [...list, item]);
flush();
list.lastElementChild.scrollIntoView();

Keep flush() for cases like that and for tests. Most handlers never need it.

Try it: add a few entries. The summary is always one behind, and the list never scrolls to the new entry. Make the summary a derived value, then flush before scrolling.