Angular Knowledge Patch

Angular Knowledge Patch

Use this skill when writing, reviewing, upgrading, or debugging modern Angular applications. Start with the breaking changes and defaults below, then open the topic reference that matches the task.

Reference index

Breaking changes and defaults

Components default to OnPush

An omitted changeDetection now means OnPush. Use the renamed eager strategy only for a component that truly requires full eager checking:

@Component({
  selector: 'legacy-widget',
  template: `...`,
  changeDetection: ChangeDetectionStrategy.Eager,
})
export class LegacyWidget {}

Audit code that mutates plain fields without a recognized notification. Prefer signals, markForCheck(), ComponentRef.setInput(), template or host listeners, or attaching an already-dirty view.

New applications are zoneless

Do not add ZoneJS as a reflex. Remove stale provideZoneChangeDetection() overrides, zone.js polyfills, and the package when migrating an application to the zoneless default. NgZone stability events do not report render timing under zoneless operation; use afterNextRender, afterEveryRender, or a DOM observer.

Reactive Forms mutations emit through form observables but do not themselves schedule a zoneless refresh. Bridge the relevant observable to a template-read signal or call markForCheck().

For server rendering, register application-owned asynchronous work with PendingTasks; router navigations and HttpClient calls are already registered.

Use the current server-route contract

Server route paths are slashless. Configure renderMode, and use getPrerenderParams for parameterized prerendering. Call inject() synchronously before any await in that callback.

export const serverRoutes: ServerRoute[] = [{
  path: 'post/:id',
  renderMode: RenderMode.Prerender,
  fallback: PrerenderFallback.Client,
  async getPrerenderParams() {
    const posts = inject(PostService);
    return (await posts.ids()).map(id => ({id}));
  },
}];

The older mode and getPrerenderPaths names belong only to the preview contract. Read the SSR reference before changing hybrid rendering, redirects, or route cleanup.

Removed and deprecated integrations

• The built-in Protractor builder and Hammer.js integration are removed.
• Experimental Jest and Web Test Runner integrations are deprecated; retained Jest suites need a community integration.
• Webpack-based Angular builders and @ngtools/webpack are deprecated.
• TestBed.getFixture() is renamed to TestBed.getLastFixture().
• ChangeDetectorRef.checkNoChanges() is removed; use fixture-level test APIs.

Security behavior is stricter

Treat SVG animation URL attributes and object[data] as security-sensitive URL contexts. Translations cannot target iframe src, translated form attributes and translated interpolated bindings are sanitized, and event attributes cannot be internationalized. Concrete-host bindings also pass through the applicable sanitizer. Do not bypass these checks to preserve old behavior.

Namespaced MathML script elements are removed and prefixed SVG script hosts are rejected.

High-value APIs

Choose the right resource primitive

Use resource for asynchronous reads driven by reactive parameters. Returning undefined from params leaves it idle; changing parameters aborts the previous load.

const user = resource({
  params: () => id() ? {id: id()} : undefined,
  loader: ({params, abortSignal}) =>
    fetch(`/api/users/${params.id}`, {signal: abortSignal})
      .then(response => response.json()),
});

Check hasValue() before value() because value() throws in the error state. reload() keeps the prior value with reloading status; set() and update() mark the value local.

Use:

• httpResource for HttpClient-backed reads with interceptors, cancellation, testing support, response-type helpers, and optional parsing.
• rxResource when an Observable loader should publish every emission.
• stream when a resource source publishes a signal of {value} or {error} items.
• resourceFromSnapshots when transforming a resource snapshot signal while preserving the resource interface.

Keep mutation commands out of read resources. To submit explicitly, copy draft state into the signal used by params; reads performed only inside loader do not become reload dependencies.

Put DOM work after rendering

Signal writes are allowed in effect; the old write opt-in is unnecessary. Root effects run before component checks and view effects run before their component is checked. Use afterRenderEffect for DOM- or query-dependent work.

afterRenderEffect({
  earlyRead: () => host().nativeElement.getBoundingClientRect(),
  write: rect => {
    host().nativeElement.style.height = `${rect().width}px`;
  },
});

Available phases are earlyRead, write, mixedReadWrite, and read; each later phase receives the prior phase result as a signal. The callback is client-only and can still run before its component hydrates.

Build forms from writable model signals

Signal Forms turn a writable model signal into a callable typed field tree:

model = signal({email: '', password: ''});
loginForm = form(this.model, path => required(path.email));

<input [formField]="loginForm.email" />

Every bindable field must exist in the initial model. Prefer empty leaf values over absent optional properties or null object branches. Track array fields by field identity so their interaction and validation state survive reordering.

Schemas support built-in, custom, cross-field, HTTP, asynchronous, and Standard Schema validation, plus reactive disabled, hidden, and readonly rules. Read the forms reference before implementing arrays, submission, reset, custom controls, or validation timing.

Use native CSS enter and leave animation

For insertion and removal, attach classes with animate.enter and animate.leave instead of introducing the legacy animation DSL:

@if (shown()) {
  <div animate.enter="enter" animate.leave="leave">Content</div>
}

Nested leave animations can run within the same component boundary.

Prefer Angular Aria for headless interactions

@angular/aria provides unstyled directives for keyboard behavior, focus, ARIA state, screen-reader support, and RTL navigation. It covers autocomplete, listbox, select, multiselect, combobox, menu, menubar, toolbar, accordion, tabs, tree, and grid patterns. Keep markup, styling, and application behavior in the app.

Use runtime bindings without wrappers

createComponent and TestBed.createComponent accept inputBinding, outputBinding, and twoWayBinding. Runtime-applied directives can have their own binding lists. NgComponentOutlet can receive an EnvironmentInjector for an isolated provider scope.

Use lazy global services intentionally

Use @Service() as the concise root-singleton form when no deeper provider configuration or constructor injection is required. Such a service can be code-split with injectAsync and optionally prefetched on idle.

private exporter = injectAsync(() => import('./report-exporter'));

Testing defaults

New projects use Vitest with a Node DOM emulator. ng test watches by default. Configure global Angular providers through a default-exported providersFile; use setupFiles for general initialization. Real-browser execution supports the Playwright or WebdriverIO Vitest providers.

Prefer await fixture.whenStable() in zoneless tests. Repeated unconditional fixture.detectChanges() can conceal missing change notifications; exhaustive no-change checks can expose them.

The CLI owns important portions of the Vitest configuration even when runnerConfig points to a custom file. Read the testing reference for target options, browser naming, migration limitations, and output files.

Upgrade checklist

1. Match Angular, Node.js, TypeScript, and RxJS using the exact compatibility row for the destination minor line.
2. Move across majors one at a time with ng update, and ensure the destination is still supported.
3. Run supplied migrations, including strict template checking and replacements for deprecated router-testing or styling constructs.
4. Re-test locale-sensitive output, URL sanitization, translated attributes, server redirects, and hydration transfer caching.
5. Verify zoneless notifications, pending SSR tasks, OnPush assumptions, and unit tests without relying on forced detection.
6. Replace removed integrations and plan exits from deprecated test and build tooling.

Preview APIs can change outside the normal deprecation guarantees. Confirm their current signatures before adopting them in long-lived libraries.