@terajs/reactivity

Fine-grained reactive primitives for Terajs.

Most application code can import these APIs through @terajs/app, but this package is the canonical leaf package for signals, effects, computed values, and DX helpers.

Core surface

• signal(initialValue, options?): callable reactive accessor with .set() and .update()
• state(initialValue): explicit .get() / .set() state container
• computed(fn, options?): lazy derived value with .get()
• effect(fn): tracked side effect
• reactive(object), ref(value), model()
• DX helpers: watch(), watchEffect(), onEffectCleanup(), dispose(), contract()
• memo helpers: memo(), markStatic(), shallowRef()
• runtime mode helpers: isServer(), setRuntimeMode()

signal() vs state()

Terajs ships both forms on purpose:

• signal() is a callable accessor and is the common app-facing primitive
• state() is an explicit getter/setter container used where that shape is clearer or already established

import { computed, effect, signal, state } from "@terajs/reactivity";

const count = signal(0);
const legacyCount = state(0);
const doubled = computed(() => count() * 2);

effect(() => {
  console.log(count(), legacyCount.get(), doubled.get());
});

count.set(1);
legacyCount.set(1);

Observability and DevTools

The reactivity package is wired into the shared debug core.

• signals register reactive metadata
• computed values register ownership and recomputation events
• effects participate in the dependency graph
• DevTools can inspect graph state and runtime updates without app-specific logging glue

Notes

• computed() currently returns an object with .get(), not a callable accessor.
• signal() can carry metadata options such as scope, instance, key, and source location for diagnostics.
• For app-level docs, prefer the @terajs/app import path unless you are deliberately working at the leaf-package level.