Releases · stackblitz/alien-signals

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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