feat(computed): add computed/extendedComputed with access to previous…

… computed value

libs/ngxtension/computed/README.md

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+# ngxtension/computed
+
+Secondary entry point of `ngxtension`. It can be used by importing from `ngxtension/computed`.

libs/ngxtension/computed/ng-package.json

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

libs/ngxtension/computed/project.json

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

libs/ngxtension/computed/src/computed.spec.ts

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+import { Component, signal } from '@angular/core';
+import { TestBed } from '@angular/core/testing';
+import { computed } from './computed';
+
+describe(computed.name, () => {
+	@Component({
+		standalone: true,
+		template: '',
+	})
+	class Test {
+		count = signal(0);
+		multiplier = signal(1);
+
+		result = computed<number>((currentValue) => {
+			if (this.multiplier() % 2 === 0) {
+				return this.count() * this.multiplier();
+			}
+			return currentValue;
+		});
+
+		track = 0;
+		trackedResult = computed<number>((currentValue) => {
+			this.track += 1;
+			if (this.multiplier() % 2 === 0) {
+				return this.count() * this.multiplier();
+			}
+			return currentValue;
+		});
+	}
+
+	function setup() {
+		const fixture = TestBed.createComponent(Test);
+		fixture.detectChanges();
+		return fixture.componentInstance;
+	}
+
+	it('should work properly', () => {
+		const component = setup();
+
+		expect(component.result()).toEqual(undefined);
+
+		component.count.set(1);
+		expect(component.result()).toEqual(undefined);
+
+		component.multiplier.set(2);
+		expect(component.result()).toEqual(2);
+
+		component.multiplier.set(3);
+		expect(component.result()).toEqual(2);
+	});
+
+	it('should track dep properly', () => {
+		const component = setup();
+
+		// kick off computed
+		expect(component.trackedResult()).toEqual(undefined);
+		// track increments
+		expect(component.track).toEqual(1);
+
+		// set count only while multipler is still odd
+		component.count.set(1);
+		// result is still undefined
+		expect(component.trackedResult()).toEqual(undefined);
+		// computed is not reinvoked
+		expect(component.track).toEqual(1);
+
+		// set count only again
+		component.count.set(2);
+		// result is still undefined
+		expect(component.trackedResult()).toEqual(undefined);
+		// computed is not reinvoked
+		expect(component.track).toEqual(1);
+
+		// set multiplier to an even number
+		component.multiplier.set(2);
+		// result is now 4 (multipler * count)
+		expect(component.trackedResult()).toEqual(4);
+		// computed is invoked because multiplier changes
+		expect(component.track).toEqual(2);
+
+		// set multiplier back to an odd number
+		component.multiplier.set(3);
+		// result is 4 because it returns the currentValue
+		expect(component.trackedResult()).toEqual(4);
+		// computed is reinvoked because multiplier changes
+		expect(component.track).toEqual(3);
+
+		// set count while multiplier is an odd number
+		component.count.set(3);
+		// result is still 4 because it returns the currentValue
+		expect(component.trackedResult()).toEqual(4);
+		// computed is not reinvoked
+		expect(component.track).toEqual(3);
+	});
+});

libs/ngxtension/computed/src/computed.ts

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+import type { CreateComputedOptions } from '@angular/core';
+import { computed as ngComputed, signal, untracked } from '@angular/core';
+
+export function computed<TValue>(
+	computedCallback: (currentValue: TValue) => TValue,
+	options?: CreateComputedOptions<TValue>
+) {
+	if (!options) {
+		options = { equal: Object.is };
+	}
+
+	const currentValue = signal<TValue>(undefined!, { equal: Object.is });
+	return ngComputed(() => {
+		const computedValue = computedCallback(untracked(currentValue));
+		untracked(() => {
+			currentValue.set(computedValue);
+		});
+		return computedValue;
+	}, options);
+}
+
+export const extendedComputed = computed;

libs/ngxtension/computed/src/index.ts

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+export * from './computed';

tsconfig.base.json

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 			"ngxtension/click-outside": [
 				"libs/ngxtension/click-outside/src/index.ts"
 			],
+			"ngxtension/computed": ["libs/ngxtension/computed/src/index.ts"],
 			"ngxtension/computed-from": [
 				"libs/ngxtension/computed-from/src/index.ts"
 			],