feat: add effectOnceIf helper function

docs/src/content/contributors/lorenzo-dianni.json

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+{
+	"name": "Lorenzo D'Ianni",
+	"twitter": "https://x.com/lorenzodianni",
+	"linkedin": "https://www.linkedin.com/in/lorenzo-d-ianni-3990bba6/",
+	"github": "https://github.com/lorenzodianni"
+}

docs/src/content/docs/utilities/Signals/effect-once-if.md

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+---
+title: effectOnceIf
+description: ngxtension/effect-once-if
+entryPoint: effect-once-if
+badge: stable
+contributors: ['lorenzo-dianni']
+---
+
+`effectOnceIf` is a helper function that allows you to create an effect that will be executed only once if a certain condition occurs.
+
+## Usage
+
+```ts
+@Component({})
+class Example {
+	count = signal(0);
+
+	effectOnceIfRef = effectOnceIf(
+		// condition function: if it returns a truly value, the execution function will run
+		() => this.count() > 3,
+		// execution function: will run only once
+		(valueReturnedFromCondition, onCleanup) => {
+			console.log(
+				`triggered with value returned: ${valueReturnedFromCondition}`,
+			);
+			onCleanup(() => console.log('cleanup'));
+		},
+	);
+}
+
+// example.count.set(1);
+//    -> nothing happens
+// example.count.set(4);
+//    -> log: triggered with value returned: true
+//    -> log: cleanup
+// example.count.set(6);
+//    -> nothing happens
+```

libs/ngxtension/effect-once-if/README.md

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+# ngxtension/effect-once-if
+
+Secondary entry point of `ngxtension`. It can be used by importing from `ngxtension/effect-once-if`.

libs/ngxtension/effect-once-if/ng-package.json

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+{
+	"lib": {
+		"entryFile": "src/index.ts"
+	}
+}

libs/ngxtension/effect-once-if/project.json

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+{
+	"name": "ngxtension/effect-once-if",
+	"$schema": "../../../node_modules/nx/schemas/project-schema.json",
+	"projectType": "library",
+	"sourceRoot": "libs/ngxtension/effect-once-if/src",
+	"targets": {
+		"test": {
+			"executor": "@nx/jest:jest",
+			"outputs": ["{workspaceRoot}/coverage/{projectRoot}"],
+			"options": {
+				"jestConfig": "libs/ngxtension/jest.config.ts",
+				"testPathPattern": ["effect-once-if"],
+				"passWithNoTests": true
+			},
+			"configurations": {
+				"ci": {
+					"ci": true,
+					"codeCoverage": true
+				}
+			}
+		},
+		"lint": {
+			"executor": "@nx/eslint:lint",
+			"outputs": ["{options.outputFile}"]
+		}
+	}
+}

libs/ngxtension/effect-once-if/src/effect-once-if.spec.ts

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+import { Component, signal } from '@angular/core';
+import { TestBed } from '@angular/core/testing';
+import { effectOnceIf } from './effect-once-if';
+
+function createTestComponent(triggerValue: number) {
+	const log: string[] = [];
+	const logCleanup: string[] = [];
+
+	@Component({ standalone: true, template: '' })
+	class Example {
+		count = signal(0);
+
+		ref = effectOnceIf(
+			() => this.count() === triggerValue,
+			(value, onCleanup) => {
+				log.push(`received ${triggerValue}: ${value}`);
+				onCleanup(() => {
+					logCleanup.push(`cleaning effect with condition ${triggerValue}`);
+				});
+			},
+		);
+	}
+
+	return { component: Example, log, logCleanup };
+}
+
+describe(effectOnceIf.name, () => {
+	it('should run effect once and cleanup', () => {
+		const test = createTestComponent(2);
+		const fixture = TestBed.createComponent(test.component);
+		fixture.detectChanges();
+		expect(test.log).toEqual([]);
+		expect(test.logCleanup).toEqual([]);
+
+		fixture.componentInstance.count.set(1);
+		fixture.detectChanges();
+		expect(test.log).toEqual([]);
+		expect(test.logCleanup).toEqual([]);
+
+		fixture.componentInstance.count.set(2);
+		fixture.detectChanges();
+		expect(test.log).toEqual(['received 2: true']);
+		expect(test.logCleanup).toEqual(['cleaning effect with condition 2']);
+
+		fixture.componentInstance.count.set(3);
+		fixture.detectChanges();
+		expect(test.log).toEqual(['received 2: true']);
+		expect(test.logCleanup).toEqual(['cleaning effect with condition 2']);
+	});
+
+	it('should run effect once and cleanup on init', () => {
+		const test = createTestComponent(0);
+		const fixture = TestBed.createComponent(test.component);
+		fixture.detectChanges();
+		expect(test.log).toEqual(['received 0: true']);
+		expect(test.logCleanup).toEqual(['cleaning effect with condition 0']);
+
+		fixture.componentInstance.count.set(1);
+		fixture.detectChanges();
+		expect(test.log).toEqual(['received 0: true']);
+		expect(test.logCleanup).toEqual(['cleaning effect with condition 0']);
+	});
+});

libs/ngxtension/effect-once-if/src/effect-once-if.ts

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+import {
+	CreateEffectOptions,
+	effect,
+	EffectCleanupRegisterFn,
+	EffectRef,
+	runInInjectionContext,
+	untracked,
+} from '@angular/core';
+import { assertInjector } from 'ngxtension/assert-injector';
+
+export function effectOnceIf<T = any>(
+	condition: () => T,
+	execution: (
+		valueFromCondition: NonNullable<T>,
+		onCleanup: EffectCleanupRegisterFn,
+	) => void,
+	options?: Omit<CreateEffectOptions, 'allowSignalWrites' | 'manualCleanup'>,
+): EffectRef {
+	const assertedInjector = assertInjector(effectOnceIf, options?.injector);
+	return runInInjectionContext(assertedInjector, () => {
+		const effectRef = effect((onCleanup) => {
+			const hasCondition = condition();
+			if (hasCondition) {
+				untracked(() => execution(hasCondition, onCleanup));
+				effectRef.destroy();
+			}
+		}, options);
+		return effectRef;
+	});
+}
+
+export type EffectOnceIfConditionFn<T> = Parameters<typeof effectOnceIf<T>>[0];
+export type EffectOnceIfExecutionFn<T> = Parameters<typeof effectOnceIf<T>>[1];
+export type EffectOnceIfOptions<T> = Parameters<typeof effectOnceIf<T>>[2];

libs/ngxtension/effect-once-if/src/index.ts

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+export * from './effect-once-if';

tsconfig.base.json

@@ -68,6 +68,9 @@
 				"libs/ngxtension/derived-async/src/index.ts"
 			],
 			"ngxtension/derived-from": ["libs/ngxtension/derived-from/src/index.ts"],
+			"ngxtension/effect-once-if": [
+				"libs/ngxtension/effect-once-if/src/index.ts"
+			],
 			"ngxtension/filter-array": ["libs/ngxtension/filter-array/src/index.ts"],
 			"ngxtension/filter-nil": ["libs/ngxtension/filter-nil/src/index.ts"],
 			"ngxtension/gestures": ["libs/ngxtension/gestures/src/index.ts"],