Solidjs V2

SolidJS 2.0

Solid 2.0 is not React and not Solid 1.x. Both priors are the dominant bug sources in generated code. When in doubt, distrust pattern-matching and check references/cheatsheet.md (official, ships with the package) or the installed typings in node_modules.

Step 0 — confirm this is actually a v2 project

Check before applying anything below:

• package.json: solid-js major is 2 (e.g. 2.0.0-rc.x), and/or @solidjs/web is a dependency.
• tsconfig.json: "jsxImportSource": "@solidjs/web".

If solid-js is 1.x (imports like solid-js/web, solid-js/store), stop — these rules do not apply; that's a Solid 1.x project. If the task is to convert it, use the solidjs-v2-migration skill instead.

Prereleases drift: when docs and the installed package disagree, trust the typings in node_modules (solid-js, @solidjs/web, @solidjs/signals).

The ten rules that prevent most bugs

1. Reads lag writes. Updates apply on the next microtask: setCount(1); count() still returns 0. Synchronous point: flush(). batch() does not exist.
2. createEffect takes two functions — (compute, apply, options?). Compute tracks and returns a value; apply does side effects (untracked) and may return a cleanup. The 1.x single-callback form throws. on(), createComputed, initial-value args: all gone.
3. Never write signals/stores or invoke an action inside a reactive scope (memo, compute, component body) — throws in dev. Define actions there if useful, but invoke/write from event handlers, effect callbacks, actions, or onSettled. untrack() suppresses read tracking but does not exempt writes. Derive instead of writing back.
4. No top-level reactive reads in component bodies and no destructured props — warns, value goes stale. Read via props.x inside JSX / memos / effect computes; untrack(() => ...) for deliberate one-shots.
5. Props are values, not accessors. Call site: <X v={count()} />, never <X v={count} />. Child: props.v, never function X({ v }). This stays reactive — the compiler turns v={count()} into { get v() { return count() } }, so reading props.v in the child re-runs count() in the child's tracking scope. Passing the accessor (v={count} + props.v()) to "keep reactivity" is a misconception: props have always been getters in Solid (1.x and 2.0 alike — value-passing didn't change), so it's unnecessary and just forces every consumer to call a function.
6. Async is just a computation: const user = createMemo(() => fetchUser(id())) — no createResource. Wrap consumers in <Loading fallback={...}>; errors go to <Errored>. In-flight-change indicators: isPending(() => user()) — fires for changed inputs and affects() declarations; a bare refresh() is normally quiet. await refresh(source) waits for the settled re-ask; until(predicate) waits for a truthy live-source acknowledgement.
7. Store setters take a draft: setStore(s => { s.a.b = 1; }) (produce is the default). Store APIs (createStore, reconcile, snapshot…) are exported from solid-js — solid-js/store does not exist.
8. List rendering is For with keying modes — <Index> is gone. Callback shapes differ per mode (see references); keyed={false} gives (itemAccessor, plainIndex). Fixed-count rendering: <Repeat>.
9. Lifecycle: onSettled(() => { ...; return cleanup; }) replaces onMount/onCleanup for component-level setup-and-teardown. It's a leaf owner — no primitives or onCleanup inside.
10. Imports moved: @solidjs/web for render/hydrate/Portal/Dynamic (not solid-js/web); jsxImportSource: "@solidjs/web"; DOM attributes are lowercase (tabindex); class takes object/array forms (classList is gone); directives are ref={factory(opts)} (use: is gone).

Reference routing

Read the file matching the task before writing code in that area:

Failure modes

• App renders nothing / mount seems stuck → pending async outside a Loading boundary defers the root mount; check the console for ASYNC_OUTSIDE_LOADING_BOUNDARY.
• Dev throws/warns with a diagnostic code (REACTIVE_WRITE_IN_OWNED_SCOPE, STRICT_READ_UNTRACKED, …) → table of codes and fixes at the bottom of references/reactivity.md. Fix the cause; never silence with ownedWrite for app state.
• Test asserts stale values → missing flush() after writes, or reactive code created without an owner (createRoot in tests).
• An API from docs/examples doesn't exist → prereleases drift; verify against installed typings and prefer them over any doc, including these references.