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alien-signals
Advanced tools
This project explores a push-pull based signal algorithm. Its current implementation is similar to or related to certain other frontend projects:
We impose some constraints (such as not using Array/Set/Map and disallowing function recursion) to ensure performance. We found that under these conditions, maintaining algorithmic simplicity offers more significant improvements than complex scheduling strategies.
Even though Vue 3.4 is already optimized, alien-signals is still noticeably faster. (I wrote code for both, and since they share similar algorithms, they’re quite comparable.)
Benchmark repo: https://github.com/transitive-bullshit/js-reactivity-benchmark
I spent considerable time optimizing Vue 3.4’s reactivity system, gaining experience along the way. Since Vue 3.5 switched to a pull-based algorithm similar to Preact, I decided to continue researching a push-pull based implementation in a separate project. Our end goal is to implement fully incremental AST parsing and virtual code generation in Vue language tools, based on alien-signals.
import { signal, computed, effect } from 'alien-signals';
const count = signal(1);
const doubleCount = computed(() => count() * 2);
effect(() => {
console.log(`Count is: ${count()}`);
}); // Console: Count is: 1
console.log(doubleCount()); // 2
count(2); // Console: Count is: 2
console.log(doubleCount()); // 4
import { signal, effect, effectScope } from 'alien-signals';
const count = signal(1);
const stopScope = effectScope(() => {
effect(() => {
console.log(`Count in scope: ${count()}`);
}); // Console: Count in scope: 1
});
count(2); // Console: Count in scope: 2
stopScope();
count(3); // No console output
You can reuse alien-signals’ core algorithm via createReactiveSystem()
to build your own signal API. For implementation examples, see:
.get()
& .set()
methods like the Signals proposal)propagate
and checkDirty
functionsIn order to eliminate recursive calls and improve performance, we record the last link node of the previous loop in propagate
and checkDirty
functions, and implement the rollback logic to return to this node.
This results in code that is difficult to understand, and you don't necessarily get the same performance improvements in other languages, so we record the original implementation without eliminating recursive calls here for reference.
propagate
function propagate(link: Link): void {
do {
const sub = link.sub;
let flags = sub.flags;
if (flags & (ReactiveFlags.Mutable | ReactiveFlags.Watching)) {
if (!(flags & (ReactiveFlags.RecursedCheck | ReactiveFlags.Recursed | ReactiveFlags.Dirty | ReactiveFlags.Pending))) {
sub.flags = flags | ReactiveFlags.Pending;
} else if (!(flags & (ReactiveFlags.RecursedCheck | ReactiveFlags.Recursed))) {
flags = ReactiveFlags.None;
} else if (!(flags & ReactiveFlags.RecursedCheck)) {
sub.flags = (flags & ~ReactiveFlags.Recursed) | ReactiveFlags.Pending;
} else if (!(flags & (ReactiveFlags.Dirty | ReactiveFlags.Pending)) && isValidLink(link, sub)) {
sub.flags = flags | ReactiveFlags.Recursed | ReactiveFlags.Pending;
flags &= ReactiveFlags.Mutable;
} else {
flags = ReactiveFlags.None;
}
if (flags & ReactiveFlags.Watching) {
notify(sub);
}
if (flags & ReactiveFlags.Mutable) {
const subSubs = sub.subs;
if (subSubs !== undefined) {
propagate(subSubs);
}
}
}
link = link.nextSub!;
} while (link !== undefined);
}
checkDirty
function checkDirty(link: Link, sub: ReactiveNode): boolean {
do {
const dep = link.dep;
const depFlags = dep.flags;
if (sub.flags & ReactiveFlags.Dirty) {
return true;
} else if ((depFlags & (ReactiveFlags.Mutable | ReactiveFlags.Dirty)) === (ReactiveFlags.Mutable | ReactiveFlags.Dirty)) {
if (update(dep)) {
const subs = dep.subs!;
if (subs.nextSub !== undefined) {
shallowPropagate(subs);
}
return true;
}
} else if ((depFlags & (ReactiveFlags.Mutable | ReactiveFlags.Pending)) === (ReactiveFlags.Mutable | ReactiveFlags.Pending)) {
if (checkDirty(dep.deps!, dep)) {
if (update(dep)) {
const subs = dep.subs!;
if (subs.nextSub !== undefined) {
shallowPropagate(subs);
}
return true;
}
} else {
dep.flags = depFlags & ~ReactiveFlags.Pending;
}
}
link = link.nextDep!;
} while (link !== undefined);
return false;
}
FAQs
The lightest signal library.
The npm package alien-signals receives a total of 1,917,004 weekly downloads. As such, alien-signals popularity was classified as popular.
We found that alien-signals demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 1 open source maintainer collaborating on the project.
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