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 precisely its subscribers — doubled, and any DOM node displaying either value. No other part of the page is visited.
This is the substance of the zero-VDOM model: the dependency graph already records what must be updated, so there is nothing to diff.
Why it matters
Without diffing there is no per-update reconciliation pass whose cost scales with the size of the view. Update cost scales with what actually changed.