A signal is a value plus the set of computations that read it. When the value changes, only those computations re-run — and in OTF Web, a computation is often a single DOM update.
JSX
let count = $state(0); const doubled = $derived(count * 2);
Reading count inside a binding subscribes that binding to it. Reassigning count notifies exactly its subscribers — doubled, and any DOM node showing either value. Nothing else on the page is visited.
That's the whole idea behind "zero-VDOM": the dependency graph already knows what to update, so there's nothing to diff.
Why it matters
No diffing means no per-frame reconciliation work that scales with your view size — updates scale with what actually changed.