From c062613a8e0727a57dc466cf4268bee1c2d4bcbb Mon Sep 17 00:00:00 2001
From: thomas <thomas.ext@squadracer.com>
Date: Mon, 2 Oct 2023 21:42:47 +0200
Subject: [PATCH] feat(challenge36): add solution on trackby

---
 README.md                                     |   2 +-
 .../performance/ngfor-optimize/.eslintrc.json |  36 +++++++
 apps/performance/ngfor-optimize/README.md     |  13 +++
 .../performance/ngfor-optimize/jest.config.ts |  22 ++++
 apps/performance/ngfor-optimize/project.json  |  99 ++++++++++++++++++
 .../ngfor-optimize/src/app/app.component.ts   |  58 ++++++++++
 .../ngfor-optimize/src/app/app.config.ts      |   6 ++
 .../ngfor-optimize/src/app/generateList.ts    |  15 +++
 .../ngfor-optimize/src/app/list.service.ts    |  44 ++++++++
 .../src/app/person-list.component.ts          |  37 +++++++
 .../ngfor-optimize/src/app/person.model.ts    |   4 +
 .../ngfor-optimize/src/assets/.gitkeep        |   0
 .../ngfor-optimize/src/favicon.ico            | Bin 0 -> 15086 bytes
 .../performance/ngfor-optimize/src/index.html |  13 +++
 apps/performance/ngfor-optimize/src/main.ts   |   7 ++
 .../ngfor-optimize/src/styles.scss            |   5 +
 .../ngfor-optimize/src/test-setup.ts          |   2 +
 .../ngfor-optimize/tailwind.config.js         |  14 +++
 .../ngfor-optimize/tsconfig.app.json          |  10 ++
 .../ngfor-optimize/tsconfig.editor.json       |   7 ++
 apps/performance/ngfor-optimize/tsconfig.json |  32 ++++++
 .../ngfor-optimize/tsconfig.spec.json         |  15 +++
 challenge-number.json                         |   4 +-
 .../angular-performance/36-ngfor-optimize.md  |  54 ++++++++++
 docs/src/content/docs/index.mdx               |   4 +-
 .../app/src/app/app.component.ts__tmpl__      |   2 +-
 .../cli/src/generators/challenge/generator.ts |   2 +-
 libs/cli/src/generators/readme/generator.ts   |  25 +++--
 libs/shared/directives/src/index.ts           |   1 +
 .../directives/src/lib/track-by.directive.ts  |  51 +++++++++
 30 files changed, 564 insertions(+), 20 deletions(-)
 create mode 100644 apps/performance/ngfor-optimize/.eslintrc.json
 create mode 100644 apps/performance/ngfor-optimize/README.md
 create mode 100644 apps/performance/ngfor-optimize/jest.config.ts
 create mode 100644 apps/performance/ngfor-optimize/project.json
 create mode 100644 apps/performance/ngfor-optimize/src/app/app.component.ts
 create mode 100644 apps/performance/ngfor-optimize/src/app/app.config.ts
 create mode 100644 apps/performance/ngfor-optimize/src/app/generateList.ts
 create mode 100644 apps/performance/ngfor-optimize/src/app/list.service.ts
 create mode 100644 apps/performance/ngfor-optimize/src/app/person-list.component.ts
 create mode 100644 apps/performance/ngfor-optimize/src/app/person.model.ts
 create mode 100644 apps/performance/ngfor-optimize/src/assets/.gitkeep
 create mode 100644 apps/performance/ngfor-optimize/src/favicon.ico
 create mode 100644 apps/performance/ngfor-optimize/src/index.html
 create mode 100644 apps/performance/ngfor-optimize/src/main.ts
 create mode 100644 apps/performance/ngfor-optimize/src/styles.scss
 create mode 100644 apps/performance/ngfor-optimize/src/test-setup.ts
 create mode 100644 apps/performance/ngfor-optimize/tailwind.config.js
 create mode 100644 apps/performance/ngfor-optimize/tsconfig.app.json
 create mode 100644 apps/performance/ngfor-optimize/tsconfig.editor.json
 create mode 100644 apps/performance/ngfor-optimize/tsconfig.json
 create mode 100644 apps/performance/ngfor-optimize/tsconfig.spec.json
 create mode 100644 docs/src/content/docs/challenges/angular-performance/36-ngfor-optimize.md
 create mode 100644 libs/shared/directives/src/lib/track-by.directive.ts

diff --git a/README.md b/README.md
index a98d91be1..84456c4d7 100644
--- a/README.md
+++ b/README.md
@@ -24,7 +24,7 @@ If you would like to propose a challenge, this project is open source, so feel f
 
 ## Challenges
 
-Check [all 35 challenges](https://angular-challenges.vercel.app/)
+Check [all 36 challenges](https://angular-challenges.vercel.app/)
 
 ## Contributors ✨
 
diff --git a/apps/performance/ngfor-optimize/.eslintrc.json b/apps/performance/ngfor-optimize/.eslintrc.json
new file mode 100644
index 000000000..bf8df1428
--- /dev/null
+++ b/apps/performance/ngfor-optimize/.eslintrc.json
@@ -0,0 +1,36 @@
+{
+  "extends": ["../../../.eslintrc.json"],
+  "ignorePatterns": ["!**/*"],
+  "overrides": [
+    {
+      "files": ["*.ts"],
+      "rules": {
+        "@angular-eslint/directive-selector": [
+          "error",
+          {
+            "type": "attribute",
+            "prefix": "app",
+            "style": "camelCase"
+          }
+        ],
+        "@angular-eslint/component-selector": [
+          "error",
+          {
+            "type": "element",
+            "prefix": "app",
+            "style": "kebab-case"
+          }
+        ]
+      },
+      "extends": [
+        "plugin:@nx/angular",
+        "plugin:@angular-eslint/template/process-inline-templates"
+      ]
+    },
+    {
+      "files": ["*.html"],
+      "extends": ["plugin:@nx/angular-template"],
+      "rules": {}
+    }
+  ]
+}
diff --git a/apps/performance/ngfor-optimize/README.md b/apps/performance/ngfor-optimize/README.md
new file mode 100644
index 000000000..657170429
--- /dev/null
+++ b/apps/performance/ngfor-optimize/README.md
@@ -0,0 +1,13 @@
+# NgFor Optimization
+
+> Author: Thomas Laforge
+
+### Run Application
+
+```bash
+npx nx serve performance-ngfor-optimize
+```
+
+### Documentation and Instruction
+
+Challenge documentation is [here](https://angular-challenges.vercel.app/challenges/angular-performance/36-ngfor-optimize/).
diff --git a/apps/performance/ngfor-optimize/jest.config.ts b/apps/performance/ngfor-optimize/jest.config.ts
new file mode 100644
index 000000000..5b2ccaee0
--- /dev/null
+++ b/apps/performance/ngfor-optimize/jest.config.ts
@@ -0,0 +1,22 @@
+/* eslint-disable */
+export default {
+  displayName: 'performance-ngfor-optimize',
+  preset: '../../../jest.preset.js',
+  setupFilesAfterEnv: ['<rootDir>/src/test-setup.ts'],
+  coverageDirectory: '../../../coverage/apps/performance/ngfor-optimize',
+  transform: {
+    '^.+\\.(ts|mjs|js|html)$': [
+      'jest-preset-angular',
+      {
+        tsconfig: '<rootDir>/tsconfig.spec.json',
+        stringifyContentPathRegex: '\\.(html|svg)$',
+      },
+    ],
+  },
+  transformIgnorePatterns: ['node_modules/(?!.*\\.mjs$)'],
+  snapshotSerializers: [
+    'jest-preset-angular/build/serializers/no-ng-attributes',
+    'jest-preset-angular/build/serializers/ng-snapshot',
+    'jest-preset-angular/build/serializers/html-comment',
+  ],
+};
diff --git a/apps/performance/ngfor-optimize/project.json b/apps/performance/ngfor-optimize/project.json
new file mode 100644
index 000000000..c34d04f5b
--- /dev/null
+++ b/apps/performance/ngfor-optimize/project.json
@@ -0,0 +1,99 @@
+{
+  "name": "performance-ngfor-optimize",
+  "$schema": "../../../node_modules/nx/schemas/project-schema.json",
+  "projectType": "application",
+  "prefix": "app",
+  "sourceRoot": "apps/performance/ngfor-optimize/src",
+  "tags": [],
+  "targets": {
+    "build": {
+      "executor": "@angular-devkit/build-angular:browser",
+      "outputs": ["{options.outputPath}"],
+      "options": {
+        "outputPath": "dist/apps/performance/ngfor-optimize",
+        "index": "apps/performance/ngfor-optimize/src/index.html",
+        "main": "apps/performance/ngfor-optimize/src/main.ts",
+        "polyfills": ["zone.js"],
+        "tsConfig": "apps/performance/ngfor-optimize/tsconfig.app.json",
+        "assets": [
+          "apps/performance/ngfor-optimize/src/favicon.ico",
+          "apps/performance/ngfor-optimize/src/assets"
+        ],
+        "styles": [
+          "apps/performance/ngfor-optimize/src/styles.scss",
+          "./node_modules/@angular/material/prebuilt-themes/indigo-pink.css"
+        ],
+        "scripts": [],
+        "allowedCommonJsDependencies": ["seedrandom"]
+      },
+      "configurations": {
+        "production": {
+          "budgets": [
+            {
+              "type": "initial",
+              "maximumWarning": "500kb",
+              "maximumError": "1mb"
+            },
+            {
+              "type": "anyComponentStyle",
+              "maximumWarning": "2kb",
+              "maximumError": "4kb"
+            }
+          ],
+          "outputHashing": "all"
+        },
+        "development": {
+          "buildOptimizer": false,
+          "optimization": false,
+          "vendorChunk": true,
+          "extractLicenses": false,
+          "sourceMap": true,
+          "namedChunks": true
+        }
+      },
+      "defaultConfiguration": "production"
+    },
+    "serve": {
+      "executor": "@angular-devkit/build-angular:dev-server",
+      "configurations": {
+        "production": {
+          "browserTarget": "performance-ngfor-optimize:build:production"
+        },
+        "development": {
+          "browserTarget": "performance-ngfor-optimize:build:development"
+        }
+      },
+      "defaultConfiguration": "development"
+    },
+    "extract-i18n": {
+      "executor": "@angular-devkit/build-angular:extract-i18n",
+      "options": {
+        "browserTarget": "performance-ngfor-optimize:build"
+      }
+    },
+    "lint": {
+      "executor": "@nx/linter:eslint",
+      "outputs": ["{options.outputFile}"],
+      "options": {
+        "lintFilePatterns": [
+          "apps/performance/ngfor-optimize/**/*.ts",
+          "apps/performance/ngfor-optimize/**/*.html"
+        ]
+      }
+    },
+    "test": {
+      "executor": "@nx/jest:jest",
+      "outputs": ["{workspaceRoot}/coverage/{projectRoot}"],
+      "options": {
+        "jestConfig": "apps/performance/ngfor-optimize/jest.config.ts",
+        "passWithNoTests": true
+      },
+      "configurations": {
+        "ci": {
+          "ci": true,
+          "codeCoverage": true
+        }
+      }
+    }
+  }
+}
diff --git a/apps/performance/ngfor-optimize/src/app/app.component.ts b/apps/performance/ngfor-optimize/src/app/app.component.ts
new file mode 100644
index 000000000..58d89f4f5
--- /dev/null
+++ b/apps/performance/ngfor-optimize/src/app/app.component.ts
@@ -0,0 +1,58 @@
+import { Component, OnInit, inject } from '@angular/core';
+import { FormsModule } from '@angular/forms';
+import { MatFormFieldModule } from '@angular/material/form-field';
+import { MatInputModule } from '@angular/material/input';
+import { PersonService } from './list.service';
+import { PersonListComponent } from './person-list.component';
+
+@Component({
+  standalone: true,
+  imports: [
+    PersonListComponent,
+    FormsModule,
+    MatFormFieldModule,
+    MatInputModule,
+  ],
+  providers: [PersonService],
+  selector: 'app-root',
+  template: `
+    <h1 class="font-semibold text-center text-3xl" title="Title">
+      List of Persons
+    </h1>
+
+    <mat-form-field class="w-3/4">
+      <input
+        placeholder="Add one member to the list"
+        matInput
+        type="text"
+        [(ngModel)]="label"
+        (keydown)="handleKey($event)" />
+    </mat-form-field>
+
+    <app-person-list
+      class="max-w-2xl w-3/4"
+      [persons]="persons()"
+      (delete)="personService.deletePerson($event)"
+      (update)="personService.updatePerson($event)" />
+  `,
+  host: {
+    class: 'flex items-center flex-col gap-5',
+  },
+})
+export class AppComponent implements OnInit {
+  readonly personService = inject(PersonService);
+  readonly persons = this.personService.persons;
+
+  label = '';
+
+  ngOnInit(): void {
+    this.personService.loadPersons();
+  }
+
+  handleKey(event: any) {
+    if (event.keyCode === 13) {
+      this.personService.addPerson(this.label);
+      this.label = '';
+    }
+  }
+}
diff --git a/apps/performance/ngfor-optimize/src/app/app.config.ts b/apps/performance/ngfor-optimize/src/app/app.config.ts
new file mode 100644
index 000000000..59198e627
--- /dev/null
+++ b/apps/performance/ngfor-optimize/src/app/app.config.ts
@@ -0,0 +1,6 @@
+import { ApplicationConfig } from '@angular/core';
+import { provideAnimations } from '@angular/platform-browser/animations';
+
+export const appConfig: ApplicationConfig = {
+  providers: [provideAnimations()],
+};
diff --git a/apps/performance/ngfor-optimize/src/app/generateList.ts b/apps/performance/ngfor-optimize/src/app/generateList.ts
new file mode 100644
index 000000000..41b934e71
--- /dev/null
+++ b/apps/performance/ngfor-optimize/src/app/generateList.ts
@@ -0,0 +1,15 @@
+import { randEmail, randFirstName } from '@ngneat/falso';
+import { Person } from './person.model';
+
+export function generateList() {
+  const arr: Person[] = [];
+
+  for (let i = 0; i < 50; i++) {
+    arr.push({
+      email: randEmail(),
+      name: randFirstName(),
+    });
+  }
+
+  return arr;
+}
diff --git a/apps/performance/ngfor-optimize/src/app/list.service.ts b/apps/performance/ngfor-optimize/src/app/list.service.ts
new file mode 100644
index 000000000..e56bddef8
--- /dev/null
+++ b/apps/performance/ngfor-optimize/src/app/list.service.ts
@@ -0,0 +1,44 @@
+import { Injectable, inject, signal } from '@angular/core';
+import { randEmail, randFirstName } from '@ngneat/falso';
+import { generateList } from './generateList';
+import { Person } from './person.model';
+
+@Injectable()
+export class PersonService {
+  private readonly fakeBackend = inject(FakeBackendService);
+  readonly persons = signal<Person[]>([]);
+
+  loadPersons() {
+    this.persons.set(generateList());
+  }
+
+  deletePerson(email: string) {
+    this.persons.set(
+      this.fakeBackend
+        .returnNewList(this.persons())
+        .filter((p) => p.email !== email)
+    );
+  }
+
+  updatePerson(email: string) {
+    this.persons.set(
+      this.fakeBackend
+        .returnNewList(this.persons())
+        .map((p) => (p.email === email ? { email, name: randFirstName() } : p))
+    );
+  }
+
+  addPerson(name: string) {
+    this.persons.set([
+      { email: randEmail(), name },
+      ...this.fakeBackend.returnNewList(this.persons()),
+    ]);
+  }
+}
+
+@Injectable({ providedIn: 'root' })
+export class FakeBackendService {
+  returnNewList = (input: Person[]): Person[] => [
+    ...input.map((i) => ({ ...i })),
+  ];
+}
diff --git a/apps/performance/ngfor-optimize/src/app/person-list.component.ts b/apps/performance/ngfor-optimize/src/app/person-list.component.ts
new file mode 100644
index 000000000..69aee34d8
--- /dev/null
+++ b/apps/performance/ngfor-optimize/src/app/person-list.component.ts
@@ -0,0 +1,37 @@
+import { Component, EventEmitter, Input, Output } from '@angular/core';
+
+import { CommonModule } from '@angular/common';
+import { Person } from './person.model';
+
+@Component({
+  selector: 'app-person-list',
+  standalone: true,
+  imports: [CommonModule],
+  template: `
+    <div
+      *ngFor="let person of persons"
+      class="flex justify-between items-center border-b">
+      <h3>{{ person.name }}</h3>
+      <div class="flex gap-10 py-1">
+        <button
+          class="border rounded-md p-2 bg-blue-500 text-white"
+          (click)="update.emit(person.email)">
+          UPDATE
+        </button>
+        <button
+          class="border rounded-md p-2 bg-red-500 text-white"
+          (click)="delete.emit(person.email)">
+          DELETE
+        </button>
+      </div>
+    </div>
+  `,
+  host: {
+    class: 'w-full flex flex-col',
+  },
+})
+export class PersonListComponent {
+  @Input() persons: Person[] = [];
+  @Output() delete = new EventEmitter<string>();
+  @Output() update = new EventEmitter<string>();
+}
diff --git a/apps/performance/ngfor-optimize/src/app/person.model.ts b/apps/performance/ngfor-optimize/src/app/person.model.ts
new file mode 100644
index 000000000..0ccffbbf9
--- /dev/null
+++ b/apps/performance/ngfor-optimize/src/app/person.model.ts
@@ -0,0 +1,4 @@
+export interface Person {
+  email: string;
+  name: string;
+}
diff --git a/apps/performance/ngfor-optimize/src/assets/.gitkeep b/apps/performance/ngfor-optimize/src/assets/.gitkeep
new file mode 100644
index 000000000..e69de29bb
diff --git a/apps/performance/ngfor-optimize/src/favicon.ico b/apps/performance/ngfor-optimize/src/favicon.ico
new file mode 100644
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HcmV?d00001

diff --git a/apps/performance/ngfor-optimize/src/index.html b/apps/performance/ngfor-optimize/src/index.html
new file mode 100644
index 000000000..63fe2adcd
--- /dev/null
+++ b/apps/performance/ngfor-optimize/src/index.html
@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8" />
+    <title>performance-ngfor-optimize</title>
+    <base href="/" />
+    <meta name="viewport" content="width=device-width, initial-scale=1" />
+    <link rel="icon" type="image/x-icon" href="favicon.ico" />
+  </head>
+  <body>
+    <app-root></app-root>
+  </body>
+</html>
diff --git a/apps/performance/ngfor-optimize/src/main.ts b/apps/performance/ngfor-optimize/src/main.ts
new file mode 100644
index 000000000..514c89a08
--- /dev/null
+++ b/apps/performance/ngfor-optimize/src/main.ts
@@ -0,0 +1,7 @@
+import { bootstrapApplication } from '@angular/platform-browser';
+import { appConfig } from './app/app.config';
+import { AppComponent } from './app/app.component';
+
+bootstrapApplication(AppComponent, appConfig).catch((err) =>
+  console.error(err)
+);
diff --git a/apps/performance/ngfor-optimize/src/styles.scss b/apps/performance/ngfor-optimize/src/styles.scss
new file mode 100644
index 000000000..77e408aa8
--- /dev/null
+++ b/apps/performance/ngfor-optimize/src/styles.scss
@@ -0,0 +1,5 @@
+@tailwind base;
+@tailwind components;
+@tailwind utilities;
+
+/* You can add global styles to this file, and also import other style files */
diff --git a/apps/performance/ngfor-optimize/src/test-setup.ts b/apps/performance/ngfor-optimize/src/test-setup.ts
new file mode 100644
index 000000000..15de72a3c
--- /dev/null
+++ b/apps/performance/ngfor-optimize/src/test-setup.ts
@@ -0,0 +1,2 @@
+import '@testing-library/jest-dom';
+import 'jest-preset-angular/setup-jest';
diff --git a/apps/performance/ngfor-optimize/tailwind.config.js b/apps/performance/ngfor-optimize/tailwind.config.js
new file mode 100644
index 000000000..38183db2c
--- /dev/null
+++ b/apps/performance/ngfor-optimize/tailwind.config.js
@@ -0,0 +1,14 @@
+const { createGlobPatternsForDependencies } = require('@nx/angular/tailwind');
+const { join } = require('path');
+
+/** @type {import('tailwindcss').Config} */
+module.exports = {
+  content: [
+    join(__dirname, 'src/**/!(*.stories|*.spec).{ts,html}'),
+    ...createGlobPatternsForDependencies(__dirname),
+  ],
+  theme: {
+    extend: {},
+  },
+  plugins: [],
+};
diff --git a/apps/performance/ngfor-optimize/tsconfig.app.json b/apps/performance/ngfor-optimize/tsconfig.app.json
new file mode 100644
index 000000000..58220429a
--- /dev/null
+++ b/apps/performance/ngfor-optimize/tsconfig.app.json
@@ -0,0 +1,10 @@
+{
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "outDir": "../../../dist/out-tsc",
+    "types": []
+  },
+  "files": ["src/main.ts"],
+  "include": ["src/**/*.d.ts"],
+  "exclude": ["jest.config.ts", "src/**/*.test.ts", "src/**/*.spec.ts"]
+}
diff --git a/apps/performance/ngfor-optimize/tsconfig.editor.json b/apps/performance/ngfor-optimize/tsconfig.editor.json
new file mode 100644
index 000000000..8ae117d96
--- /dev/null
+++ b/apps/performance/ngfor-optimize/tsconfig.editor.json
@@ -0,0 +1,7 @@
+{
+  "extends": "./tsconfig.json",
+  "include": ["src/**/*.ts"],
+  "compilerOptions": {
+    "types": ["jest", "node"]
+  }
+}
diff --git a/apps/performance/ngfor-optimize/tsconfig.json b/apps/performance/ngfor-optimize/tsconfig.json
new file mode 100644
index 000000000..e85865cf5
--- /dev/null
+++ b/apps/performance/ngfor-optimize/tsconfig.json
@@ -0,0 +1,32 @@
+{
+  "compilerOptions": {
+    "target": "es2022",
+    "useDefineForClassFields": false,
+    "forceConsistentCasingInFileNames": true,
+    "strict": true,
+    "noImplicitOverride": true,
+    "noPropertyAccessFromIndexSignature": true,
+    "noImplicitReturns": true,
+    "noFallthroughCasesInSwitch": true
+  },
+  "files": [],
+  "include": [],
+  "references": [
+    {
+      "path": "./tsconfig.app.json"
+    },
+    {
+      "path": "./tsconfig.spec.json"
+    },
+    {
+      "path": "./tsconfig.editor.json"
+    }
+  ],
+  "extends": "../../../tsconfig.base.json",
+  "angularCompilerOptions": {
+    "enableI18nLegacyMessageIdFormat": false,
+    "strictInjectionParameters": true,
+    "strictInputAccessModifiers": true,
+    "strictTemplates": true
+  }
+}
diff --git a/apps/performance/ngfor-optimize/tsconfig.spec.json b/apps/performance/ngfor-optimize/tsconfig.spec.json
new file mode 100644
index 000000000..1a4817a7d
--- /dev/null
+++ b/apps/performance/ngfor-optimize/tsconfig.spec.json
@@ -0,0 +1,15 @@
+{
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "outDir": "../../dist/out-tsc",
+    "module": "commonjs",
+    "types": ["jest", "node", "@testing-library/jest-dom"]
+  },
+  "files": ["src/test-setup.ts"],
+  "include": [
+    "jest.config.ts",
+    "src/**/*.test.ts",
+    "src/**/*.spec.ts",
+    "src/**/*.d.ts"
+  ]
+}
diff --git a/challenge-number.json b/challenge-number.json
index 85b441f6f..a6d987c39 100644
--- a/challenge-number.json
+++ b/challenge-number.json
@@ -1,6 +1,6 @@
 {
-  "total": 35,
-  "🟢": 12,
+  "total": 36,
+  "🟢": 13,
   "🟠": 116,
   "🔴": 207
 }
diff --git a/docs/src/content/docs/challenges/angular-performance/36-ngfor-optimize.md b/docs/src/content/docs/challenges/angular-performance/36-ngfor-optimize.md
new file mode 100644
index 000000000..273259239
--- /dev/null
+++ b/docs/src/content/docs/challenges/angular-performance/36-ngfor-optimize.md
@@ -0,0 +1,54 @@
+---
+title: 🟢 NgFor Optimization
+description: Challenge 36 is about ...
+sidebar:
+  order: 13
+  badge: New
+---
+
+<div class="chip">Challenge #36</div>
+
+## Information
+
+In this application, we have a list of individuals that we can add, delete or update. If you open the developer Chrome panel by pressing **F12**, go to he <b>source</b> tab, and expand the element to see the list, you will notice that each time, you add, delete or update a list item, the entire DOM elements are destroyed and initialized again. (See video below).
+
+<video controls src="https://github.com/tomalaforge/angular-challenges/assets/30832608/71b90307-3ee3-42c0-a532-b67ce4f20bf6">
+</video>
+
+We can also use the <b>Angular DevTool</b> to profile our application and understand what is happening inside our application. I will show you how to do it inside the following video.
+
+<video controls src="https://github.com/tomalaforge/angular-challenges/assets/30832608/dd8108c6-1d89-4b05-9aa5-e760bd6f7f11">
+</video>
+
+:::note
+If you don't know how to use it, read [the performance introduction page](/challenges/angular-performance/) first and come back after.
+:::
+
+If you need more information about `NgFor`, I invite you to read the [documentation](https://angular.io/api/common/NgFor) first.
+
+## Statement
+
+The goal of this challenge is to understand what is causing this DOM refresh and to solve it.
+
+---
+
+:::note
+Start the project by running: `npx nx serve ngfor-optimize`.
+:::
+
+:::tip[Reminder]
+Your PR title must start with <b>Answer:36</b>.
+:::
+
+<div class="article-footer">
+  <a
+    href="https://github.com/tomalaforge/angular-challenges/pulls?q=label%3A36+label%3Aanswer"
+    alt="NgFor Optimization community solutions">
+    ❖ Community Answers
+  </a>
+  <a
+    href='https://github.com/tomalaforge/angular-challenges/pulls?q=label%3A36+label%3A"answer+author"'
+    alt="NgFor Optimization solution author">
+    ▶︎ Author Answer
+  </a>
+</div>
diff --git a/docs/src/content/docs/index.mdx b/docs/src/content/docs/index.mdx
index c7c1fe5a5..70e1f8627 100644
--- a/docs/src/content/docs/index.mdx
+++ b/docs/src/content/docs/index.mdx
@@ -23,8 +23,8 @@ hero:
 import { Card, CardGrid } from '@astrojs/starlight/components';
 
 <CardGrid>
-<Card title="35 Challenges">
-    This repository gathers 35 Challenges related to <b>Angular</b>, <b>Nx</b>, <b>RxJS</b>, <b>Ngrx</b> and <b>Typescript</b>. 
+<Card title="36 Challenges">
+    This repository gathers 36 Challenges related to <b>Angular</b>, <b>Nx</b>, <b>RxJS</b>, <b>Ngrx</b> and <b>Typescript</b>. 
     These challenges resolve around real-life issues or specific features to elevate your skills.
 </Card>
 
diff --git a/libs/cli/src/generators/challenge/files/app/src/app/app.component.ts__tmpl__ b/libs/cli/src/generators/challenge/files/app/src/app/app.component.ts__tmpl__
index 937cefb4d..d977f0989 100644
--- a/libs/cli/src/generators/challenge/files/app/src/app/app.component.ts__tmpl__
+++ b/libs/cli/src/generators/challenge/files/app/src/app/app.component.ts__tmpl__
@@ -3,7 +3,7 @@ import { Component } from '@angular/core';
 @Component({
   standalone: true,
   imports: [],
-  selector: 'lib-root',
+  selector: 'app-root',
   template: ``,
   styles: [''],
 })
diff --git a/libs/cli/src/generators/challenge/generator.ts b/libs/cli/src/generators/challenge/generator.ts
index fa3fe1776..b319f1715 100644
--- a/libs/cli/src/generators/challenge/generator.ts
+++ b/libs/cli/src/generators/challenge/generator.ts
@@ -51,7 +51,7 @@ export async function challengeGenerator(tree: Tree, options: Schema) {
     tmpl: '',
     projectName: names(options.name).name,
     title: options.title,
-    challengeNumber,
+    challengeNumber: challengeNumber + 1,
     docRepository: options.docRepository,
   });
 
diff --git a/libs/cli/src/generators/readme/generator.ts b/libs/cli/src/generators/readme/generator.ts
index db2ddc6d1..95f507c26 100644
--- a/libs/cli/src/generators/readme/generator.ts
+++ b/libs/cli/src/generators/readme/generator.ts
@@ -1,5 +1,4 @@
 import { Tree, formatFiles } from '@nx/devkit';
-import { readFile, writeFile } from 'fs/promises';
 
 const README_FILENAME = 'README.md';
 const OMIT = ['memoized', 'projection', 'testing-table', 'testing-forms'];
@@ -46,10 +45,10 @@ function findHref(href) {
 
 async function rewriteFile(tree: Tree, file: string) {
   console.log('Current file', file);
-  const buffer = await readFile(file, { encoding: 'utf-8' });
+  const buffer = tree.read(file);
 
   const regex = new RegExp(/Answer:(\d+)/);
-  const match = buffer.match(regex);
+  const match = buffer.toString().match(regex);
 
   if (!match) throw new Error('NO MATCH');
 
@@ -69,19 +68,19 @@ async function rewriteFile(tree: Tree, file: string) {
     -2
   )}/${pathElts.at(-1)}/`;
 
-  const doc = await readFile(docFile, { encoding: 'utf-8' });
+  const doc = tree.read(docFile);
 
   const regexTitle = new RegExp(/title:\s(🟢|🟠|🔴)\s(.+?)\n/);
-  const matchTitle = doc.match(regexTitle);
+  const matchTitle = doc.toString().match(regexTitle);
   const title = matchTitle[2];
 
   const regexCommand = new RegExp(/npx nx serve\s(.+?)`\s/);
-  const matchCommand = buffer.match(regexCommand);
+  const matchCommand = buffer.toString().match(regexCommand);
 
   let command = '';
   if (!matchCommand) {
     const regexOldCommand = new RegExp(/nx serve\s(.+?)\*/);
-    command = buffer.match(regexOldCommand)[1];
+    command = buffer.toString().match(regexOldCommand)[1];
   } else {
     command = matchCommand[1];
   }
@@ -103,12 +102,12 @@ npx nx serve ${command}
 Challenge documentation is [here](${link}).
 `;
 
-  await writeFile(file, finalText, { encoding: 'utf-8' });
+  tree.write(file, finalText);
 
   ///**** */
 
   const regexHref = new RegExp(/<a href=("|')(.+?)("|')/, 'g');
-  const href = buffer.match(regexHref).map(findHref);
+  const href = buffer.toString().match(regexHref).map(findHref);
 
   console.log('HREF', href);
 
@@ -150,21 +149,21 @@ Your PR title must start with <b>Answer:${number}</b>.
   }
 
   const regexHeader = new RegExp(/([\s\S]*?)\s:::note/);
-  const header = doc.match(regexHeader)[1];
+  const header = doc.toString().match(regexHeader)[1];
 
   console.log('header', header);
 
   const regexContent = new RegExp(
     /Author: Thomas Laforge([\s\S]*?)### Submitting your work/
   );
-  const matchContent = buffer.match(regexContent);
+  const matchContent = buffer.toString().match(regexContent);
 
   let content = '';
   if (!matchContent) {
     const regexOldContent = new RegExp(
       /Author: Thomas Laforge([\s\S]*?)## Submitting your work/
     );
-    content = buffer.match(regexOldContent)[1];
+    content = buffer.toString().match(regexOldContent)[1];
   } else {
     content = matchContent[1];
   }
@@ -184,7 +183,7 @@ ${content}
 ${footerText}
   `;
 
-  await writeFile(docFile, fullDocText, { encoding: 'utf-8' });
+  tree.write(docFile, fullDocText);
 }
 
 export async function readmeGenerator(tree: Tree) {
diff --git a/libs/shared/directives/src/index.ts b/libs/shared/directives/src/index.ts
index be3fd1e43..fd1b22675 100644
--- a/libs/shared/directives/src/index.ts
+++ b/libs/shared/directives/src/index.ts
@@ -1 +1,2 @@
 export * from './lib/cd-flashing.directive';
+export { NgForTrackByModule } from './lib/track-by.directive';
diff --git a/libs/shared/directives/src/lib/track-by.directive.ts b/libs/shared/directives/src/lib/track-by.directive.ts
new file mode 100644
index 000000000..47ba73a22
--- /dev/null
+++ b/libs/shared/directives/src/lib/track-by.directive.ts
@@ -0,0 +1,51 @@
+/* eslint-disable @angular-eslint/directive-selector */
+import { NgFor, NgForOf } from '@angular/common';
+import {
+  Directive,
+  Input,
+  NgIterable,
+  NgModule,
+  Provider,
+  inject,
+} from '@angular/core';
+
+@Directive({
+  selector: '[ngForTrackByProp]',
+  standalone: true,
+})
+export class NgForTrackByPropDirective<T> {
+  @Input() ngForOf!: NgIterable<T>;
+
+  @Input()
+  set ngForTrackByProp(ngForTrackBy: keyof T) {
+    // setter
+    this.ngFor.ngForTrackBy = (index: number, item: T) => item[ngForTrackBy];
+  }
+
+  private ngFor = inject(NgForOf<T>, { self: true });
+}
+
+@Directive({
+  selector: '[ngForTrackById]',
+  standalone: true,
+})
+export class NgForTrackByIdDirective<T extends { id: string | number }> {
+  @Input() ngForOf!: NgIterable<T>; // 2
+
+  private ngFor = inject(NgForOf<T>, { self: true }); // 3
+
+  constructor() {
+    this.ngFor.ngForTrackBy = (index: number, item: T) => item.id; // 4
+  }
+}
+
+export const NgForTrackByDirective: Provider[] = [
+  NgForTrackByIdDirective,
+  NgForTrackByPropDirective,
+];
+
+@NgModule({
+  imports: [NgFor, NgForTrackByDirective],
+  exports: [NgFor, NgForTrackByDirective],
+})
+export class NgForTrackByModule {}