There is a known issue in Angular 8 that causes this problem.

To address it, you can implement the following workaround:

ng update @angular/cli @angular/core --allow-dirty

Attempting to upgrade from Angular 8 to Angular 9 using the mention command resulted in an error.

After that, I decided to use the same command with the --force flag and it successfully upgraded.

ng update @angular/cli @angular/core --allow-dirty --force

I encountered a similar issue before. It seems to be a common bug in Angular 8. Instead of using dirty commands to bypass the repo check, there is a different approach you can take.

ng update @angular/cli @angular/core --allow-dirty or
ng update @angular/cli @angular/core --allow-dirty --force

However, I chose not to go down that route. Here's what I did instead...

Firstly, make sure you have committed all changes before attempting the update. Make a copy of your project in the same location and commit this copy to Git as well. Then run the following command from the original project directory:

ng update @angular/core@8 @angular/cli@8

Afterwards, you can safely delete the copied project. This method worked for me! Thank you!

It did the trick!

Try this command in terminal: sudo npm update @angular/cli @angular/core --allow-dirty --legacy-peer-deps

If you are looking to upgrade your Angular 13 project to Angular 14 (October 2022), here's a step-by-step guide:

To begin, navigate to your project directory and open the command prompt with Administrator privileges. Then, execute the following command:

ng update @angular/core@14 @angular/cli@14 --allow-dirty --force

After running the above command, you should see an output similar to the one below. Please note that the specifics may vary based on your current Angular version:

The installed Angular CLI version is outdated.
Installing a temporary Angular CLI versioned 14.2.5 for updating purposes.
√ Package installation successful.
Repository contains changes. Update modifications will merge with existing alterations.
Using npm package manager.
Gathering installed dependencies...
Located 23 dependencies.
Retrieving dependency information from registry...
    Updating package.json with dependency @angular-devkit/build-angular @ "14.2.5" (used to be "13.2.6")...
    Updating package.json with dependency @angular/cli @ "14.2.5" (used to be "13.2.6")...
    Updating package.json with dependency @angular/compiler-cli @ "14.2.5" (used to be "13.2.7")...
    Updating package.json with dependency typescript @ "4.8.4" (used to be "4.5.5")...
    Updating package.json with dependency @angular/animations @ "14.2.5" (used to be "13.2.7")...
    Updating package.json with dependency @angular/common @ "14.2.5" (used to be "13.2.7")...
    Updating package.json with dependency @angular/compiler @ "14.2.5" (used to be "13.2.7")...
    Updating package.json with dependency @angular/core @ "14.2.5" (used to be "13.2.7")...
    Updating package.json with dependency @angular/forms @ "14.2.5" (used to be "13.2.7")...
    Updating package.json with dependency @angular/platform-browser @ "14.2.5" (used to be "13.2.7")...
    Updating package.json with dependency @angular/platform-browser-dynamic @ "14.2.5" (used to be "13.2.7")...
    Updating package.json with dependency @angular/router @ "14.2.5" (used to be "13.2.7")...
UPDATE package.json (1068 bytes)
√ Packages successfully updated.
** Executing migrations for '@angular/cli' **

> Eliminate 'defaultProject' option from workspace configuration.
  The project selection will now rely on the current working directory.
UPDATE angular.json (3177 bytes)
Migration complete.

> Discard 'showCircularDependencies' option from browser and server builders.
Migration complete.

> Swap out 'defaultCollection' option in workspace config with 'schematicCollections'.
Migration complete.

> Modify version prefixes of Angular packages 'dependencies' and 'devDependencies' to '^' instead of '~'.
UPDATE package.json (1068 bytes)
√ Packages installed without errors.
Migration complete.

> Delete 'package.json' files from library projects secondary entry points.
Migration complete.

> Adjust TypeScript compilation target to 'ES2020'.
UPDATE tsconfig.json (863 bytes)
Migration complete.

** Executing migrations for '@angular/core' **

> Starting Angular version 13, `entryComponents` are no longer necessary.
Migration complete.

> In Angular version 14, the `pathMatch` property of `Routes` was updated to a strict union of the two valid options: `'full'|'prefix'`.
  Variables `Routes` and `Route` require explicit typing to prevent TypeScript inferring the property as a looser `string`.
Migration complete.

> As of Angular version 14, Forms model classes allow a type parameter, and existing instances must opt out to maintain backward compatibility.
Migration complete.

Below is the updated package.json file after completing the upgrade process:

{
  "name": "custom-project-14",
  "version": "0.0.0",
  "scripts": {
    "ng": "ng",
    "start": "ng serve",
    "build": "ng build",
    "watch": "ng build --watch --configuration development",
    "test": "ng test"
  },
  "private": true,
  "dependencies": {
    "@angular/animations": "^14.2.5",
    "@angular/common": "^14.2.5",
    "@angular/compiler": "^14.2.5",
    "@angular/core": "^14.2.5",
    "@angular/forms": "^14.2.5",
    "@angular/platform-browser": "^14.2.5",
    "@angular/platform-browser-dynamic": "^14.2.5",
    "@angular/router": "^14.2.5",
    "rxjs": "~7.5.0",
    "tslib": "^2.3.0",
    "zone.js": "~0.11.4"
  },
  "devDependencies": {
    "@angular-devkit/build-angular": "^14.2.5",
    "@angular/cli": "^14.2.5",
    "@angular/compiler-cli": "^14.2.5",
    "@types/jasmine": "~3.10.0",
    "@types/node": "^12.11.1",
    "jasmine-core": "~4.0.0",
    "karma": "~6.3.0",
    "karma-chrome-launcher": "~3.1.0",
    "karma-coverage": "~2.1.0",
    "karma-jasmine": "~4.0.0",
    "karma-jasmine-html-reporter": "~1.7.0",
    "typescript": "~4.8.4"
  }
}

My issue was resolved by simply excluding the node_modules folder in the .gitignore file. After adding it, the error disappeared completely.

Just do it. Take the leap.

git add .
git commit -m "work in progress: before making changes"

Angular simply recommends that you make a minimal "backup" of your work before updating. It's all about good habits.

To begin, make sure to review your code for any recent changes that have not been pushed to git. If there are updates, be sure to push them before proceeding. Next, close the current command prompt instance and open a fresh one before running the command again. Following these steps resolved the issue for me. Many thanks!

In various instances, this situation may arise. Ensure to either save your work or stash any modifications before re-running the specified command.

After searching everywhere, I finally found a recommendation that worked for me. I discovered it on AI and guidance websites: The warning message "Repository is not clean. Please commit or stash any changes before updating" indicates that there are uncommitted modifications in your Git repository that must be either committed or stashed before you can update Angular.

To resolve this issue, follow these steps:

Firstly, open your terminal and navigate to the directory of your Angular project.

Execute the following command in the terminal:

git status

This will display the current status of your Git repository.

If there are uncommitted changes, you have two options: You can commit them using the command :

git commit -m "commit message"

Or you can stash them by running the command:

git stash

Once you have committed or stashed your changes, run the following command :

ng update @angular/core @angular/cli

again to update Angular.

Once the update is completed, you can reapply your modifications to the updated code by executing the command:

git stash apply

If you stashed your changes, or manually merge your changes if you committed them.

Important Note: It is best practice to always commit your changes before updating any dependencies in your project. This ensures that you have a backup of your code in case anything goes wrong during the update process.