stackblitz/alien-signals v2.0.0 on GitHub

Version 2.0 rethinks and optimizes the reactive system model, with minimal impact on users who only use the surface APIs. If you extend or deeply utilize alien-signals, please pay attention to the "Reactive Model Refactor" section.

Changes to Surface APIs

Added four new APIs: getCurrentSub, setCurrentSub, getCurrentScope, setCurrentScope

Deferred Signal Value Evaluation

Differences from v1

In v1, assigning a value to a signal immediately propagated the Dirty flag, causing some computed values to be unnecessarily re-evaluated.

// v1
const src = signal(10);
const double = computed(() => src() * 2);

double(); // -> 20

src(999); // double.flags -> Dirty
src(10);  // no effect

double(); // -> 20 (recomputed unnecessarily)

In v2, assigning a value to a signal only propagates the Pending flag, reducing unnecessary recomputation. Actual evaluation occurs during the next read.

// v2
const src = signal(10);
const double = computed(() => src() * 2);

double(); // -> 20

src(999); // src.flags -> Dirty, double.flags -> Pending
src(10);  // no effect

double(); // Checks src state -> unchanged, no recomputation needed

Effect Scope Parent-Child Hierarchy

In v2, recursive cleanup is achieved through a parent-child structure:

const scope1 = effectScope(() => {
	const scope2 = effectScope(() => {
		effect(() => ...);
		computed(() => ...);
	});
});

scope1();

Calling scope1() automatically cleans up its child scope scope2.

To make scope2 independent of scope1, temporarily set activeScope = undefined manually:

const scope1 = effectScope(() => {
	const prev = setCurrentScope(undefined);
	const scope2 = effectScope(() => {
		effect(() => ...);
		computed(() => ...);
	});
	setCurrentScope(prev);
});

Reactive Model Refactor

Merged Subscriber and Dependency into ReactiveNode
Trigger unwatched(dep) when all subscribers are lost, without recursively clearing subsequent subscribers
propagate now only propagates Pending; to immediately mark Dirty, call propagate + shallowPropagate after assignment
Adjusted naming for EffectFlags and ReactiveFlags; removed unused flags

Updated Options and APIs

notifyEffect → notify
updateComputed → update
Added the unwatched option for custom handling when all subscribers are lost
Removed processEffectNotifications, processComputedUpdate, processPendingInnerEffects, updateDirtyFlag
Added unlink, checkDirty

For performance differences, please refer to js-reactivity-benchmark.

Contributors

Thanks~

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