feat: add Effect

packages/store/src/effect.ts

@@ -0,0 +1,21 @@
+import {Deps, Derived} from "./derived";
+
+export class Effect {
+  _derived: Derived<void>;
+
+  constructor(items: Deps, effectFn: () => void) {
+    this._derived = new Derived(items, () => {}, {
+      onUpdate() {
+        effectFn();
+      },
+    });
+  }
+
+  cleanup() {
+    this._derived.cleanup()
+  }
+
+  [Symbol.dispose]() {
+    this.cleanup()
+  }
+}

packages/store/src/index.ts

@@ -1,3 +1,4 @@
 export * from './derived'
+export * from './effect'
 export * from './store'
 export * from './types'

packages/store/src/tests/effect.test.ts

@@ -0,0 +1,60 @@
+import { Store } from '../store'
+import { Derived } from '../derived'
+import { expect, vi } from 'vitest'
+import {Effect} from "../effect";
+
+describe('Effect', () => {
+  test('Side effect free', () => {
+    const count = new Store(10)
+
+    const halfCount = new Derived([count], () => {
+      return count.state / 2
+    })
+
+    const doubleCount = new Derived([count], () => {
+      return count.state * 2
+    })
+
+    const sumDoubleHalfCount = new Derived([halfCount, doubleCount], () => {
+      return halfCount.state + doubleCount.state
+    })
+
+    const fn = vi.fn();
+    new Effect([sumDoubleHalfCount], () => fn(sumDoubleHalfCount.state));
+
+    count.setState(() => 20)
+
+    expect(fn).toHaveBeenNthCalledWith(1, 50)
+
+    count.setState(() => 30)
+
+    expect(fn).toHaveBeenNthCalledWith(2, 75)
+  })
+
+  /**
+   *         A
+   *        / \
+   *       B   C
+   *      / \  |
+   *     D  E  F
+   *      \ / |
+   *       \ /
+   *        G
+   */
+  test('Complex diamond dep problem', () => {
+    const a = new Store(1)
+    const b = new Derived([a], () => a.state)
+    const c = new Derived([a], () => a.state)
+    const d = new Derived([b], () => b.state)
+    const e = new Derived([b], () => b.state)
+    const f = new Derived([c], () => c.state)
+    const g = new Derived([d, e, f], () => d.state + e.state + f.state)
+
+    const fn = vi.fn();
+    new Effect([g], () => fn(g.state));
+
+    a.setState(() => 2)
+
+    expect(fn).toHaveBeenNthCalledWith(1, 6)
+  })
+})