SolidJS — fine-grained reactivity, no VDOM

One rule governs everything else: the component function runs ONCE. Reactivity does not live in re-running the body — it lives in the reads. You read state by calling a getter (count()), and Solid re-runs only the exact DOM expression or effect that read it. There is no virtual DOM and no reconciliation; JSX compiles straight to DOM nodes. If you carry React habits here (destructuring props, expecting the body to re-run, deriving state in an effect), reactivity breaks silently — the code runs, it just stops updating.

Versions: stable is solid-js 1.9.x (1.9.11/1.9.13 line). Solid 2.0 is in beta on the next npm tag with a new reactive core (@solidjs/signals), createAsync, and automatic batching. Default to 1.9.x APIs unless the task says 2.0; flag the divergence where it matters.

When to use / when not