Upgrading to Angular 20

This is a practical guide focused on what really matters when updating a real-world application: what breaks, what makes your work easier, and how you should adapt your development style.

1. The Full Story Behind Karma's Removal: Beyond a Broken Build

The immediate issue when upgrading is that ng test will fail. The reason is a fundamental change in Angular's build tools.

Why did Angular drop Karma?

With Angular 20, the default build package changes from @angular-devkit/build-angular to the new @angular/build. This new package no longer includes the Karma plugin used by legacy test setups.

The web ecosystem has moved on to faster test runners like Vitest and Jest that use modern tools like Vite and esbuild. Karma had become a bottleneck.

What the new world looks like (Vitest/Jest)

Angular's experimental test runner, now powered by Vitest, is the future. Migrating means your unit tests will run in a fast, modern Node.js-based environment.

The "temporary fix" explained

npm install @angular-devkit/build-angular --save-dev

This command forces the CLI to fall back to the old compiler that still supports Karma. It’s a compatibility bridge — but the message is clear: start planning your migration to Jest or Vitest soon.

2. Prerequisites

Before starting the update process, make sure you meet the following:

• 
  Node.js: Version 20.11.1 or later
  


• 
  TypeScript: Version 5.8 or later
  


• 
  Project backup: Commit all current changes in Git
  

3. How to Update: CLI Command and Comparison

Update Command

Make sure you're running Node.js v20.11.1 or later:

ng update @angular/cli @angular/core

If you use Angular Material:

ng update @angular/cli @angular/core @angular/material

Manual intervention required

To reinstall the old compiler with Karma support:

npm install @angular-devkit/build-angular --save-dev

This wasn't required in earlier versions but is now mandatory if you want to keep using Karma.

Compared to earlier upgrades

• 
  Angular v19: ng update just worked.
  


• 
  Angular v20: You must manually reinstall the old builder for Karma.

4. Control Flow: More Than Syntactic Sugar

@for replaces *ngFor and is a major improvement.

Old syntax

<div *ngFor="let item of items; trackBy: trackItemById">

  {{ item.name }}

</div>

New syntax

@for (item of items; track item.id) {

  <div>{{ item.name }}</div>

} @empty {

  <div>No items to display.</div>

}

• 
  track is mandatory and encourages best practices.


• 
  @empty improves DX by removing the need for separate @if.

Automated migration and performance

Use the CLI to automatically refactor templates to the new control flow syntax:

ng generate @angular/core:control-flow

General Best Practices and Further Migrations

You can also migrate to other modern Angular features:

ng generate @angular/core:standalone

ng generate @angular/core:inject

ng generate @angular/core:route-lazy-loading

ng generate @angular/core:signal-input-migration

ng generate @angular/core:signal-queries-migration

ng generate @angular/core:output-migration

These commands allow for a comprehensive update of an Angular app to leverage the latest patterns.

5. Standalone by Default: A Fundamental Architectural Shift

By explicitly listing dependencies using the imports array at the component level, each component becomes self-contained. This:

• Clarifies your architecture


• Improves tree-shaking


• Results in smaller bundles

6. Zoneless: Escaping the "Magic" of Change Detection

In a zone-less world, the UI only updates when you explicitly tell it to.

Signals are the main tool here.

mySignal.set(newValue);

This directly tells Angular to update only the DOM parts that use that signal. It’s a surgical, predictable, and high-performance approach.

7. New Naming Convention: Why It Feels Complicated

Angular 20 introduces a new official naming convention that drops traditional suffixes.

Old naming

user-profile.component.ts

auth.service.ts

highlight.directive.ts

New naming

user-profile.ts       // UI component

auth-store.ts         // state

highlight.ts          // directive

Focus on intent instead of type

user-api.ts         // HTTP requests

auth-store.ts       // reactive state

movie-card.ts       // UI component

movie-details.ts    // UI component

Naming rules

• Use dashes: user-profile.ts
  


• Match class and filename
  


• Keep .spec.ts for tests


• Avoid generic names like utils.ts
  


• 
  Co-locate related files

Feature-based folder structure

src/

├── core/

│   └── auth/

│       ├── auth-store.ts

│       ├── login.ts

│       └── register.ts

├── features/

│   └── users/

│       ├── user-profile.ts

│       ├── user-api.ts

│       └── user-settings.ts

Benefits

• Cleaner Git diffs


• Intention-oriented code


• Easier onboarding

8. Important Detail: browserslist and Browser Support

Angular 20 no longer supports Opera officially.


If you list Opera in your browserslist, you may need to remove it.

Other non-mainstream browsers may also lose support, potentially triggering warnings or build issues.