# @reckona/mreact-reactive-core

> Fine-grained reactive primitives used across mreact.

Latest version **0.0.225** (published 2026-09-15) · MIT license · 0 weekly downloads

## Install

```sh
npm install @reckona/mreact-reactive-core
pnpm add @reckona/mreact-reactive-core
yarn add @reckona/mreact-reactive-core
bun add @reckona/mreact-reactive-core
```

## Health

**Score 70/100 (B)** — status: active.

Positive: has types; esm support; no vulnerabilities; has provenance; recently updated; high maintenance score.

Warnings: low downloads; pre 1.0.

## Facts

| | |
|---|---|
| Version | 0.0.225 |
| Published | 2026-09-15 |
| First published | 2026-05-16 |
| Weekly downloads | 0 |
| License | MIT |
| TypeScript types | bundled |
| Module format | ESM |
| Dependencies | 0 |
| Unpacked size | 389.5 KB |
| Known vulnerabilities | 0 |
| Install scripts | no |
| Provenance | attested (GitHub Actions) |
| GitHub stars | 0 |
| Maintainers | tatsuokaniwa |
| Keywords | jsx, mreact, primitives, reactivity, signals, typescript |

## Links

- npm: https://www.npmjs.com/package/@reckona/mreact-reactive-core
- Repository: https://github.com/t-k/mreact
- Homepage: https://github.com/t-k/mreact/tree/main/packages/reactive-core#readme
- Issues: https://github.com/t-k/mreact/issues
- npm.io page: https://npm.io/package/@reckona/mreact-reactive-core

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## Recent versions

- 0.0.225 (latest) — 2026-09-15
- 0.0.224 — 2026-09-15
- 0.0.223 — 2026-09-13
- 0.0.222 — 2026-09-13
- 0.0.221 — 2026-09-12
- 0.0.220 — 2026-09-12
- 0.0.219 — 2026-09-12
- 0.0.218 — 2026-09-12
- 0.0.217 — 2026-09-12
- 0.0.216 — 2026-09-10
- 0.0.215 — 2026-09-09
- 0.0.214 — 2026-09-09
- 0.0.213 — 2026-09-07
- 0.0.212 — 2026-09-06
- 0.0.211 — 2026-09-06
- … 209 more at https://npm.io/package/@reckona/mreact-reactive-core/versions

## README

# @reckona/mreact-reactive-core

`@reckona/mreact-reactive-core` provides the fine-grained reactive primitives
used across mreact. It is independent from the DOM and can be used by stores,
forms, query observers, and compiled runtime code.

## Basic Usage

```ts
import { batchAsync, cell, computed, effect } from "@reckona/mreact-reactive-core";

const count = cell(0);
const doubled = computed(() => count.get() * 2);
const selected = computed(() => ({ parity: count.get() % 2 }), {
  equals: (previous, next) => previous.parity === next.parity,
});

const dispose = effect(() => {
  console.log(doubled.get());
});

await batchAsync(async () => {
  count.set(1);
  await Promise.resolve();
  count.set(2);
});

selected.get();
dispose();
```

Use `setValue()` when the cell's value is callable and must be stored literally. Use `update()` when the next value should be derived from the previous value; the compatibility `set()` method continues to support both existing forms.

```ts
const handler = cell<() => void>(() => {});
handler.setValue(() => console.log("stored handler"));
handler.update((previous) => () => previous());
```

## Core APIs

- `cell()` creates a writable reactive value.
- `Cell.setValue(value)` writes a literal value without interpreting a function value as an updater.
- `Cell.update(updater)` applies an updater function exactly once.
- `computed()` creates a derived readonly value. Pass `{ equals }` or an equality function as the second argument to skip downstream notifications for equivalent results.
- `effect()` runs side effects when dependencies change.
- `batch()` groups updates into one flush.
- `batchAsync()` groups updates across `await` points into one flush. Use it only around intentionally scoped async work because reactive flushes are deferred until the callback settles.
- `untrack()` reads values without subscribing.
- `createCleanupScope()` creates a DOM-independent LIFO owner for effects, observers, timers, and other disposers. `runWithCleanupScope(scope, callback)` binds automatic reactive registrations only for the synchronous callback; register resources explicitly with `scope.register()` when ownership crosses an `await`.

## Update Scheduling

`cell.set()` updates the stored value immediately and propagates `computed` invalidation synchronously, but effects (including the DOM bindings emitted by the compiler) run in a single microtask scheduled at the first update. Reads through `.get()` always observe the latest value even before that flush runs.

Because browsers drain the microtask queue before any rendering steps, this scheduling is compatible with `document.startViewTransition()`: a `cell.set()` made inside the update callback is committed to the DOM before the browser captures the new-state snapshot, so no `flushSync` wrapper is required.

```ts
document.startViewTransition(() => {
  selectedMediaId.set(mediaId);
});
```

If you need the DOM committed synchronously before the current task continues, for example to measure layout right after an update, wrap the update in `flushSync` from the React DOM-compatible entrypoint (`react-dom` in mreact apps, `@reckona/mreact-dom` standalone), which drains pending reactive computations before returning. Updates deferred through `startTransition` or `useDeferredValue` run on a macrotask scheduler and are not guaranteed to land inside a view transition capture.

`batchAsync()` keeps effect flushing suspended for the full callback, including every awaited step, then releases the queued work once when the callback resolves or rejects. Use it for short transaction-style updates where intermediate effects would be misleading; avoid wrapping long I/O or user interaction flows because observers will not see effects until the batch finishes, even though direct `.get()` reads still see the latest cell values.

## Testing

`@reckona/mreact-reactive-core/testing` exports `flushMicrotasks()` and
`flushEffects()` for deterministic tests.

---
_Source: https://npm.io/package/@reckona/mreact-reactive-core · Machine-readable twin of the npm.io package page. Health data is recomputed on every publish._