feat: add trigger() function

README.md

@@ -96,6 +96,47 @@ stopScope();
 count(3); // No console output
 ```
 
+#### Manual Triggering
+
+The `trigger()` function allows you to manually trigger updates for downstream dependencies when you've directly mutated a signal's value without using the signal setter:
+
+```ts
+import { signal, computed, trigger } from 'alien-signals';
+
+const arr = signal<number[]>([]);
+const length = computed(() => arr().length);
+
+console.log(length()); // 0
+
+// Direct mutation doesn't automatically trigger updates
+arr().push(1);
+console.log(length()); // Still 0
+
+// Manually trigger updates
+trigger(arr);
+console.log(length()); // 1
+```
+
+You can also trigger multiple signals at once:
+
+```ts
+import { signal, computed, trigger } from 'alien-signals';
+
+const src1 = signal<number[]>([]);
+const src2 = signal<number[]>([]);
+const total = computed(() => src1().length + src2().length);
+
+src1().push(1);
+src2().push(2);
+
+trigger(() => {
+  src1();
+  src2();
+});
+
+console.log(total()); // 2
+```
+
 #### Creating Your Own Surface API
 
 You can reuse alien-signals’ core algorithm via `createReactiveSystem()` to build your own signal API. For implementation examples, see:

src/index.ts

@@ -182,6 +182,32 @@ export function effectScope(fn: () => void): () => void {
 	return effectScopeOper.bind(e);
 }
 
+export function trigger(fn: () => void) {
+	const sub: ReactiveNode = {
+		deps: undefined,
+		depsTail: undefined,
+		flags: ReactiveFlags.Watching,
+	};
+	const prevSub = setActiveSub(sub);
+	try {
+		fn();
+	} finally {
+		setActiveSub(prevSub);
+		do {
+			const link = sub.deps!;
+			const dep = link.dep;
+			unlink(link, sub);
+			if (dep.subs !== undefined) {
+				propagate(dep.subs);
+				shallowPropagate(dep.subs);
+			}
+		} while (sub.deps !== undefined);
+		if (!batchDepth) {
+			flush();
+		}
+	}
+}
+
 function updateComputed(c: Computed): boolean {
 	++cycle;
 	c.depsTail = undefined;

tests/trigger.spec.ts

@@ -0,0 +1,46 @@
+import { expect, test } from 'vitest';
+import { computed, effect, trigger, signal } from '../src';
+
+test('should trigger updates for dependent computed signals', () => {
+	const arr = signal<number[]>([]);
+	const length = computed(() => arr().length);
+
+	expect(length()).toBe(0);
+	arr().push(1);
+	trigger(arr);
+	expect(length()).toBe(1);
+});
+
+test('should trigger updates for the second source signal', () => {
+	const src1 = signal<number[]>([]);
+	const src2 = signal<number[]>([]);
+	const length = computed(() => src2().length);
+
+	expect(length()).toBe(0);
+	src2().push(1);
+	trigger(() => {
+		src1();
+		src2();
+	});
+	expect(length()).toBe(1);
+});
+
+test('should trigger effect once', () => {
+	const src1 = signal<number[]>([]);
+	const src2 = signal<number[]>([]);
+
+	let triggers = 0;
+
+	effect(() => {
+		triggers++;
+		src1();
+		src2();
+	});
+
+	expect(triggers).toBe(1);
+	trigger(() => {
+		src1();
+		src2();
+	});
+	expect(triggers).toBe(2);
+});