Core

Core is the foundation of the reactive runtime. It handles dependency tracking, computation scheduling, owner lifecycles, and error boundaries. It does not depend on Store, Async, DOM, or JSX.

API Groups

Basic Reactivity

• access(value): if an accessor is passed, run it and return the result; otherwise return the original value.
• createSignal(initial, options?): create [getter, setter].
• createEffect(fn, options?): create a side effect that automatically tracks dependencies.
• createComputed(fn, options?): semantic alias of createEffect.
• createMemo(fn, initial?, options?): create a cached derived value.
• createWatch(source, fn, options?): watch one or more sources and receive new and previous values.
• createSelector(source, equals?): create a selected-key predicate.

Scheduling

• batch(fn): merge multiple synchronous updates.
• untrack(fn): read without collecting dependencies.
• flushSync(fn?): synchronously flush the normal effect queue.
• startTransition(fn): put updates into the lower-priority transition queue.

Lifecycle

• createRoot(fn): create a root owner, suitable for manual mounting and disposal.
• createScope(fn?): create a manually runnable and disposable scope.
• onCleanup(fn): register a cleanup function on the current owner.
• onDispose(fn): semantic alias of onCleanup.
• onMount(fn): run a mount callback in a microtask.
• getOwner(): get the current owner.

Error Handling

• createErrorBoundary(fn, fallback?): create an error-boundary scope.
• catchError(fn, fallback): catch synchronous errors and return a fallback.

Solid-like Semantics Boundary

vanilla-signal provides Solid-like reactive primitives, but it is not the Solid component runtime. For a full lifecycle and scheduling comparison, see Solid-like but not Solid.

Key boundaries:

• createEffect runs once immediately by default; createComputed is a semantic alias of createEffect.
• onCleanup binds to the current owner. Without an owner, it cannot be cleaned up automatically and will warn in development.
• onMount uses microtask scheduling and is not a true DOM-mounted hook.
• createErrorBoundary does not render the fallback automatically.
• startTransition is only a lower-priority effect queue, not a full concurrency model.

Example

JavaScript
import { createEffect, createMemo, createSignal } from 'vanilla-signal';const [count, setCount] = createSignal(0);const doubled = createMemo(() => count() * 2);createEffect(() => {  console.log(doubled());});setCount(2);

Module Boundaries

• Core can be depended on by other modules.
• Core does not access the DOM directly.
• Core does not create Store proxies.
• Core does not process JSX/templates.