feat(signals): add signalMethod (#4597)

Closes #4581

Co-authored-by: Tim Deschryver <28659384+timdeschryver@users.noreply.github.com>
Co-authored-by: Marko Stanimirović <markostanimirovic95@gmail.com>

Author: 3 people

modules/signals/spec/signal-method.spec.ts

@@ -0,0 +1,201 @@
+import { signalMethod } from '../src';
+import { TestBed } from '@angular/core/testing';
+import {
+  createEnvironmentInjector,
+  EnvironmentInjector,
+  runInInjectionContext,
+  signal,
+} from '@angular/core';
+
+describe('signalMethod', () => {
+  const createAdder = (processingFn: (value: number) => void) =>
+    TestBed.runInInjectionContext(() => signalMethod<number>(processingFn));
+
+  it('processes a non-signal input', () => {
+    let a = 1;
+    const adder = createAdder((value) => (a += value));
+    adder(2);
+    expect(a).toBe(3);
+  });
+
+  it('processes a signal input', () => {
+    let a = 1;
+    const summand = signal(1);
+    const adder = createAdder((value) => (a += value));
+
+    adder(summand);
+    expect(a).toBe(1);
+
+    TestBed.flushEffects();
+    expect(a).toBe(2);
+
+    summand.set(2);
+    summand.set(2);
+    TestBed.flushEffects();
+    expect(a).toBe(4);
+
+    TestBed.flushEffects();
+    expect(a).toBe(4);
+  });
+
+  it('throws if is a not created in an injection context', () => {
+    expect(() => signalMethod<void>(() => void true)).toThrowError();
+  });
+
+  describe('destroying signalMethod', () => {
+    it('stops signal tracking, when signalMethod gets destroyed', () => {
+      let a = 1;
+      const summand = signal(1);
+      const adder = createAdder((value) => (a += value));
+      adder(summand);
+
+      summand.set(2);
+      TestBed.flushEffects();
+      expect(a).toBe(3);
+
+      adder.destroy();
+
+      summand.set(2);
+      TestBed.flushEffects();
+      expect(a).toBe(3);
+    });
+
+    it('can also destroy a signalMethod that processes non-signal inputs', () => {
+      const adder = createAdder(() => void true);
+      expect(() => adder(1).destroy()).not.toThrowError();
+    });
+
+    it('stops tracking all signals on signalMethod destroy', () => {
+      let a = 1;
+      const summand1 = signal(1);
+      const summand2 = signal(2);
+      const adder = createAdder((value) => (a += value));
+      adder(summand1);
+      adder(summand2);
+
+      summand1.set(2);
+      summand2.set(3);
+      TestBed.flushEffects();
+      expect(a).toBe(6);
+
+      adder.destroy();
+
+      summand1.set(2);
+      summand2.set(3);
+      TestBed.flushEffects();
+      expect(a).toBe(6);
+    });
+
+    it('does not cause issues if destroyed signalMethodFn contains destroyed effectRefs', () => {
+      let a = 1;
+      const summand1 = signal(1);
+      const summand2 = signal(2);
+      const adder = createAdder((value) => (a += value));
+
+      const childInjector = createEnvironmentInjector(
+        [],
+        TestBed.inject(EnvironmentInjector)
+      );
+
+      adder(summand1, { injector: childInjector });
+      adder(summand2);
+
+      TestBed.flushEffects();
+      expect(a).toBe(4);
+      childInjector.destroy();
+
+      summand1.set(2);
+      summand2.set(2);
+      TestBed.flushEffects();
+
+      adder.destroy();
+      expect(a).toBe(4);
+    });
+
+    it('uses the provided injector (source injector) on creation', () => {
+      let a = 1;
+      const sourceInjector = createEnvironmentInjector(
+        [],
+        TestBed.inject(EnvironmentInjector)
+      );
+      const adder = signalMethod((value: number) => (a += value), {
+        injector: sourceInjector,
+      });
+      const value = signal(1);
+
+      adder(value);
+      TestBed.flushEffects();
+
+      sourceInjector.destroy();
+      value.set(2);
+      TestBed.flushEffects();
+
+      expect(a).toBe(2);
+    });
+
+    it('prioritizes the provided caller injector over source injector', () => {
+      let a = 1;
+      const callerInjector = createEnvironmentInjector(
+        [],
+        TestBed.inject(EnvironmentInjector)
+      );
+      const sourceInjector = createEnvironmentInjector(
+        [],
+        TestBed.inject(EnvironmentInjector)
+      );
+      const adder = signalMethod((value: number) => (a += value), {
+        injector: sourceInjector,
+      });
+      const value = signal(1);
+
+      TestBed.runInInjectionContext(() => {
+        adder(value, { injector: callerInjector });
+      });
+      TestBed.flushEffects();
+      expect(a).toBe(2);
+
+      sourceInjector.destroy();
+      value.set(2);
+      TestBed.flushEffects();
+
+      expect(a).toBe(4);
+    });
+
+    it('prioritizes the provided injector over source and caller injector', () => {
+      let a = 1;
+      const callerInjector = createEnvironmentInjector(
+        [],
+        TestBed.inject(EnvironmentInjector)
+      );
+      const sourceInjector = createEnvironmentInjector(
+        [],
+        TestBed.inject(EnvironmentInjector)
+      );
+      const providedInjector = createEnvironmentInjector(
+        [],
+        TestBed.inject(EnvironmentInjector)
+      );
+
+      const adder = signalMethod((value: number) => (a += value), {
+        injector: sourceInjector,
+      });
+      const value = signal(1);
+
+      runInInjectionContext(callerInjector, () =>
+        adder(value, { injector: providedInjector })
+      );
+      TestBed.flushEffects();
+      expect(a).toBe(2);
+
+      sourceInjector.destroy();
+      value.set(2);
+      TestBed.flushEffects();
+      expect(a).toBe(4);
+
+      callerInjector.destroy();
+      value.set(1);
+      TestBed.flushEffects();
+      expect(a).toBe(5);
+    });
+  });
+});

modules/signals/src/index.ts

@@ -1,5 +1,6 @@
 export { deepComputed } from './deep-computed';
 export { DeepSignal } from './deep-signal';
+export { signalMethod } from './signal-method';
 export { signalState, SignalState } from './signal-state';
 export { signalStore } from './signal-store';
 export { signalStoreFeature, type } from './signal-store-feature';

modules/signals/src/signal-method.ts

@@ -0,0 +1,66 @@
+import {
+  assertInInjectionContext,
+  effect,
+  EffectRef,
+  inject,
+  Injector,
+  isSignal,
+  Signal,
+  untracked,
+} from '@angular/core';
+
+type SignalMethod<Input> = ((
+  input: Input | Signal<Input>,
+  config?: { injector?: Injector }
+) => EffectRef) &
+  EffectRef;
+
+export function signalMethod<Input>(
+  processingFn: (value: Input) => void,
+  config?: { injector?: Injector }
+): SignalMethod<Input> {
+  if (!config?.injector) {
+    assertInInjectionContext(signalMethod);
+  }
+
+  const watchers: EffectRef[] = [];
+  const sourceInjector = config?.injector ?? inject(Injector);
+
+  const signalMethodFn = (
+    input: Input | Signal<Input>,
+    config?: { injector?: Injector }
+  ): EffectRef => {
+    if (isSignal(input)) {
+      const instanceInjector =
+        config?.injector ?? getCallerInjector() ?? sourceInjector;
+
+      const watcher = effect(
+        (onCleanup) => {
+          const value = input();
+          untracked(() => processingFn(value));
+          onCleanup(() => watchers.splice(watchers.indexOf(watcher), 1));
+        },
+        { injector: instanceInjector }
+      );
+      watchers.push(watcher);
+
+      return watcher;
+    } else {
+      processingFn(input);
+      return { destroy: () => void true };
+    }
+  };
+
+  signalMethodFn.destroy = () =>
+    watchers.forEach((watcher) => watcher.destroy());
+
+  return signalMethodFn;
+}
+
+function getCallerInjector(): Injector | null {
+  try {
+    return inject(Injector);
+  } catch {
+    return null;
+  }
+}