@magnet/signal

Signal primitives for Magnet, with three interchangeable adapters exposing the same API: state, computed, effect, isSignal, and flush.

• tc39 — built on the signal-polyfill TC39 proposal polyfill. Effects are scheduled on a microtask and drained with flush().
• preact — built on @preact/signals-core. Leaner per-signal memory and synchronous effects, so flush() is a no-op.
• alien — built on alien-signals. The lightest implementation, with synchronous effects, so flush() is a no-op.

Install

JSR

deno add jsr:@magnet/signal

npm via JSR

npx jsr add @magnet/signal

npm

npm install @magnet-js/signal

API

All primitives are exposed under the tc39, preact, and alien namespaces:

import { preact } from "@magnet/signal";

const { computed, effect, isSignal, state } = preact;

const count = state(0);
const doubled = computed(() => count.get() * 2);

effect(() => {
  console.log("count:", count.get());
});

count.set(1); // logs "count: 1"

state(initialValue)

Creates a writable signal.

computed(computer)

Creates a read-only signal derived from other signals.

effect(callback)

Runs a side effect whenever its signal dependencies change. The callback may return a cleanup function. In the tc39 adapter the implementation is pretty much copy-pasted from Rob Eisenberg's eloquent write-up of the TC39 signals proposal; the clarity of that post made this straightforward.

isSignal(value)

Returns true for signal values created by the adapter in use.

License

MIT © 2026 Fernando G. Vilar.