angular-developer

Angular Developer Skill (v20)

Purpose

This skill provides comprehensive Angular v20 reference documentation scraped directly from the official v20.angular.dev docs. Use it for any Angular development task — writing components, debugging, architecting features, optimizing performance, or following best practices.

How to Use

When the user is working on an Angular task, identify which topic applies and read the corresponding reference file before responding. Multiple reference files may apply to a single task — read all relevant ones.

Reference Files

All reference files are located in references/ relative to this SKILL.md.

In-depth Guides

Topic	File	When to read
Signals — Overview	references/signals/overview.md	signal(), computed(), effect(), untracked(), equality functions, OnPush integration
Signals — linkedSignal	references/signals/linked-signal.md	linkedSignal(), dependent writable state, source+computation form, previous value
Signals — resource	references/signals/resource.md	resource(), async reactivity, params, loader, abort, reload, ResourceStatus, httpResource
Components — Overview	references/components/overview.md	Component anatomy, @Component decorator, metadata, standalone components, imports, host element, view, component tree
Components — Selectors	references/components/selectors.md	Type/attribute/class selectors, :not, combining selectors, selector prefixes, attribute selector use-cases
Components — Styling	references/components/styling.md	Inline vs file styles, ViewEncapsulation (Emulated/ShadowDom/None), :host, ::ng-deep, <style> in templates, external style refs
Components — Inputs	references/components/inputs.md	Signal input(), input.required(), transforms, aliases, model() for two-way, @Input decorator, getters/setters
Components — Outputs	references/components/outputs.md	Signal output(), emitting data, aliases, programmatic subscribe, @Output/EventEmitter
Components — Content Projection	references/components/content-projection.md	<ng-content>, multiple slots with select, fallback content, ngProjectAs
Components — Host Elements	references/components/host-elements.md	host property, attribute/class/style/event bindings, @HostBinding/@HostListener, binding collisions, CSS custom properties, HostAttributeToken
Components — Lifecycle	references/components/lifecycle.md	All lifecycle hooks order and details, ngOnChanges/SimpleChanges, DestroyRef, afterNextRender/afterEveryRender phases
Components — Queries	references/components/queries.md	viewChild/viewChildren, contentChild/contentChildren, required queries, locators, read option, descendants, @ViewChild/@ContentChild/QueryList
Components — DOM APIs	references/components/dom-apis.md	ElementRef, render callbacks, Renderer2, when/when-not to use DOM APIs, XSS risk of innerHTML
Components — Inheritance	references/components/inheritance.md	Extending components/directives, inherited metadata, forwarding DI deps, overriding lifecycle methods
Components — Programmatic Rendering	references/components/programmatic-rendering.md	NgComponentOutlet, ViewContainerRef.createComponent, lazy-loading, inputBinding/outputBinding/twoWayBinding, popup pattern with createComponent + hostElement
Components — Advanced Config	references/components/advanced-configuration.md	ChangeDetectionStrategy.OnPush, preserveWhitespaces, CUSTOM_ELEMENTS_SCHEMA
Components — Custom Elements	references/components/elements.md	@angular/elements, createCustomElement(), input→attribute mapping, output→custom event, typings with NgElement/WithProperties
Templates — Overview	references/templates/overview.md	Template syntax overview, differences from HTML, what topics templates cover
Templates — Binding	references/templates/binding.md	Text interpolation {{ }}, property [], attribute [attr.], CSS class/style bindings, signal-based updates
Templates — Event Listeners	references/templates/event-listeners.md	(event) syntax, $event, key modifiers, preventDefault, custom event plugins via EVENT_MANAGER_PLUGINS
Templates — Two-Way Binding	references/templates/two-way-binding.md	[()] banana-in-a-box, ngModel with FormsModule, component two-way binding with model()
Templates — Control Flow	references/templates/control-flow.md	@if/@else if/@else, as alias, @for with track, contextual vars, @empty, @switch
Templates — Pipes	references/templates/pipes.md	Built-in pipes, | operator, chaining, parameters, pure vs impure, custom pipes with @Pipe decorator
Templates — ng-content	references/templates/ng-content.md	Content projection, <ng-content /> slot, parent→child content rendering
Templates — ng-template	references/templates/ng-template.md	Template fragments, TemplateRef, #ref on ng-template, NgTemplateOutlet, ViewContainerRef.createEmbeddedView, context params, structural directives
Templates — ng-container	references/templates/ng-container.md	Grouping without DOM nodes, NgComponentOutlet, NgTemplateOutlet, structural directives, DI injection via container
Templates — Variables	references/templates/variables.md	@let local vars, scope, non-reassignable, template reference vars #name, exportAs, use with queries
Templates — @defer	references/templates/defer.md	Deferrable views, lazy loading, @placeholder/@loading/@error, triggers (idle/viewport/interaction/hover/immediate/timer/when), prefetch, testing, SSR/HMR notes
Templates — Expression Syntax	references/templates/expression-syntax.md	Supported/unsupported literals, globals, operators, optional chaining quirk, no declarations, statement vs expression differences
Templates — Whitespace	references/templates/whitespace.md	Default whitespace collapsing, preserveWhitespaces, &ngsp; entity
Directives — Overview	references/directives/overview.md	Built-in directives, NgClass, NgStyle, NgModel, NgIf, NgFor (trackBy), NgSwitch, <ng-container>
Directives — Attribute Directives	references/directives/attribute-directives.md	Custom attribute directives, ElementRef, host event bindings, input() for passing values, NgNonBindable
Directives — Structural Directives	references/directives/structural-directives.md	<ng-template>, shorthand * syntax, microsyntax grammar, creating structural directives, TemplateRef/ViewContainerRef, template type guards (ngTemplateGuard_, ngTemplateContextGuard)
Directives — Composition API	references/directives/directive-composition-api.md	hostDirectives, including/aliasing inputs and outputs, composing directives on directives, execution order, DI with host directives
Directives — NgOptimizedImage	references/directives/image-optimization.md	NgOptimizedImage, ngSrc, priority, fill mode, width/height, placeholders, srcset, loaders (built-in and custom), loaderParams, LCP optimization
Dependency Injection — Overview	references/dependency-injection/overview.md	DI concepts, what services are, inject() function, valid injection contexts
Dependency Injection — Creating Services	references/dependency-injection/creating-and-using-services.md	ng generate service, @Injectable, providedIn: 'root', injecting into components and services
Dependency Injection — Defining Providers	references/dependency-injection/defining-dependency-providers.md	InjectionToken, useClass/useValue/useFactory/useExisting, multi, provider scopes (app/component/route), provide* library pattern
Dependency Injection — Injection Context	references/dependency-injection/injection-context.md	What contexts allow inject(), runInInjectionContext, assertInInjectionContext, NG0203 error
Dependency Injection — Hierarchical Injectors	references/dependency-injection/hierarchical-dependency-injection.md	EnvironmentInjector vs ElementInjector, resolution rules, modifiers (optional/self/skipSelf/host), providers vs viewProviders, logical template tree, use-case scenarios
Dependency Injection — Lightweight Tokens	references/dependency-injection/lightweight-injection-tokens.md	Token retention problem, abstract class pattern, useExisting, tree-shaking for libraries
Dependency Injection — DI in Action	references/dependency-injection/di-in-action.md	ElementRef for DOM access, forwardRef() for circular dependencies
Routing — Overview	references/routing/overview.md	What Angular Router is, the three parts of routing (routes/outlets/links), available features overview
Routing — Define Routes	references/routing/define-routes.md	Routes, static/parameterized/wildcard paths, provideRouter, loadComponent lazy loading, redirects, page titles, TitleStrategy, route-level providers, static data, nested/child routes
Routing — Outlets	references/routing/show-routes-with-outlets.md	RouterOutlet, nested outlets, named secondary outlets, outlet lifecycle events (activate/deactivate/attach/detach), routerOutletData/ROUTER_OUTLET_DATA
Routing — Navigation	references/routing/navigate-to-routes.md	RouterLink, absolute vs relative paths, string vs array syntax, router.navigate(), router.navigateByUrl(), relativeTo, replaceUrl
Routing — Read Route State	references/routing/read-route-state.md	ActivatedRoute, route snapshots, route params, query params, matrix params, RouterLinkActive, routerLinkActiveOptions, ariaCurrentWhenActive
Routing — Redirects	references/routing/redirecting-routes.md	redirectTo, pathMatch: 'prefix'/'full', conditional redirects with RedirectFunction
Routing — Guards	references/routing/route-guards.md	CanActivate, CanActivateChild, CanDeactivate, CanMatch, guard return types, UrlTree/RedirectCommand, applying guards, ng generate guard
Routing — Resolvers	references/routing/data-resolvers.md	ResolveFn, resolve route config, accessing data via ActivatedRoute or withComponentInputBinding, error handling (withNavigationErrorHandler, RedirectCommand), parent→child resolver data
Routing — Lifecycle & Events	references/routing/lifecycle-and-events.md	All router events in order, subscribing to Router.events, withDebugTracing, loading indicators, analytics, error handling patterns
Routing — Testing	references/routing/testing.md	RouterTestingHarness, testing route params/guards/outlets/nested routes/query params, best practices (don't mock Angular Router)
Routing — Common Tasks	references/routing/common-router-tasks.md	withComponentInputBinding, 404 page, link parameters array, LocationStrategy, PathLocationStrategy vs HashLocationStrategy, <base href>
Routing — UrlMatcher	references/routing/routing-with-urlmatcher.md	UrlMatcher, custom route matching functions, UrlSegment, posParams, use cases (social handles, version URLs)
Routing — Rendering Strategies	references/routing/rendering-strategies.md	CSR vs SSG vs SSR trade-offs, decision matrix, hydration overview
Routing — Customizing Behavior	references/routing/customizing-route-behavior.md	withRouterConfig options (canceledNavigationResolution, onSameUrlNavigation, paramsInheritanceStrategy, urlUpdateStrategy, defaultQueryParamsHandling), RouteReuseStrategy, preloading strategies, UrlHandlingStrategy, custom matchers
Routing — Reference	references/routing/router-reference.md	Complete router events table, all router terminology, <base href>, HashLocationStrategy
Routing — View Transitions	references/routing/route-transition-animations.md	withViewTransitions, View Transitions API integration, CSS animation customization, onViewTransitionCreated, skipTransition()
Forms — Overview	references/forms/overview.md	Choosing between reactive vs template-driven, key differences, common foundation classes (FormControl/FormGroup/FormArray/ControlValueAccessor), data flow, mutability, testing comparison
Forms — Reactive Forms	references/forms/reactive-forms.md	FormControl, FormGroup, FormArray, FormBuilder, setValue/patchValue, formControlName/formGroupName/formArrayName, events observable, unified state change events, type guard utilities (isFormControl etc.)
Forms — Typed Forms	references/forms/typed-forms.md	Strictly typed reactive forms (Angular 14+), nullability, nonNullable, explicit type params, FormRecord, UntypedFormGroup/UntypedFormControl, NonNullableFormBuilder
Forms — Template-Driven	references/forms/template-driven-forms.md	NgModel, NgForm, NgModelGroup, two-way binding with [(ngModel)], #ref="ngModel", control state CSS classes (ng-valid/ng-dirty/ng-touched), ngSubmit, form reset
Forms — Validation	references/forms/form-validation.md	Built-in validators, custom sync/async validators (ValidatorFn/AsyncValidatorFn), NG_VALIDATORS/NG_ASYNC_VALIDATORS, cross-field validation, control status CSS classes, updateOn (change/blur/submit), ngNativeValidate
Forms — Dynamic Forms	references/forms/dynamic-forms.md	Metadata-driven form generation, QuestionBase pattern, QuestionControlService, @switch on controlType, computed() signal for FormGroup, runtime add/remove controls
HTTP Client — Overview	references/http-client/overview.md	What HttpClient provides, feature summary
HTTP Client — Setup	references/http-client/setup.md	provideHttpClient, withFetch, withInterceptors, withInterceptorsFromDi, withRequestsMadeViaParent, withJsonpSupport, XSRF options, NgModule equivalents
HTTP Client — Making Requests	references/http-client/making-requests.md	GET/POST/PUT/DELETE, typed responses, responseType, params, headers, observe, progress events, error handling, timeouts, advanced fetch options (cache/priority/mode/credentials/redirect/referrer/integrity), cold Observables, best practices
HTTP Client — httpResource	references/http-client/http-resource.md	httpResource() reactive wrapper, signal-based status/response, response types, Zod/Valibot parse option, testing
HTTP Client — Interceptors	references/http-client/interceptors.md	Functional interceptors, withInterceptors, response interception, cloning requests, inject() in interceptors, HttpContextToken, synthetic responses, redirect info, DI-based interceptors
HTTP Client — Testing	references/http-client/testing.md	provideHttpClientTesting, HttpTestingController, expectOne/match/expectNone, flushing, error testing, testing interceptors
Server-Side & Hybrid Rendering — Overview	references/ssr-hydration/overview.md	Summary of SSR/SSG/CSR strategies and guide links
Server-Side & Hybrid Rendering — SSR	references/ssr-hydration/ssr.md	ng new --ssr, ng add @angular/ssr, RenderMode, server routing, parameterized prerendering, fallback strategies, headers/status codes, server-compatible components, DOCUMENT token, REQUEST/RESPONSE_INIT, HttpClient transfer cache, Node.js/non-Node.js server config
Server-Side & Hybrid Rendering — Hydration	references/ssr-hydration/hydration.md	provideClientHydration, event replay (withEventReplay), DOM constraints, ngSkipHydration, i18n hydration, app stability, third-party library issues
Server-Side & Hybrid Rendering — Incremental Hydration	references/ssr-hydration/incremental-hydration.md	withIncrementalHydration, hydrate triggers (on idle/viewport/interaction/hover/immediate/timer, when, never), nested blocks, @placeholder requirements
Testing — Overview	references/testing/overview.md	ng test, Jasmine/Karma setup, CLI config, karma.conf.js, CI testing with ChromeHeadless
Testing — Code Coverage	references/testing/code-coverage.md	--code-coverage, coverage reports, enforcing minimums with karma.conf.js check property
Testing — Services	references/testing/services.md	Testing services with/without TestBed, spies, TestBed.inject(), fakeAsync/tick, waitForAsync, HttpClientTestingModule, HttpTestingController
Testing — Components Basics	references/testing/components-basics.md	ComponentFixture, createComponent(), detectChanges(), nativeElement, DebugElement, By.css()
Testing — Components Scenarios	references/testing/components-scenarios.md	Component binding, auto change detection, dispatchEvent(), external templates, service dependencies, fakeAsync, nested components, overrideComponent, page objects, waitForAsync
Testing — Attribute Directives	references/testing/attribute-directives.md	Test component pattern, By.directive(), :not selector, injector access, DebugElement.properties/styles/providerTokens
Testing — Pipes	references/testing/pipes.md	Isolated pipe tests (no TestBed needed), DOM tests that verify pipe integration in templates
i18n — Overview	references/i18n/overview.md	i18n vs l10n concepts, localization workflow summary, what the full i18n pipeline looks like
i18n — Add Package	references/i18n/add-package.md	ng add @angular/localize, --use-at-runtime, effect on package.json and tsconfig
i18n — Locale IDs	references/i18n/locale-id.md	Unicode locale ID format, BCP 47, CLDR, setting sourceLocale in angular.json
i18n — Format Data	references/i18n/format-data-locale.md	DatePipe, CurrencyPipe, DecimalPipe, PercentPipe, LOCALE_ID, overriding locale per-pipe
i18n — Prepare Component	references/i18n/prepare.md	i18n attribute, i18n-{attr}, $localize, metadata format meaning|description@@id, ICU plural/select/nested expressions
i18n — Translation Files	references/i18n/translation-files.md	ng extract-i18n, output formats (XLIFF/JSON/ARB/XMB), creating per-locale files, XLIFF <trans-unit> structure, translating plurals/select/nested
i18n — Merge	references/i18n/merge.md	"localize" option in angular.json, ng build --localize, locale-specific configs, ng serve single-locale limit, i18nMissingTranslation warning levels
i18n — Deploy	references/i18n/deploy.md	Subdirectory per locale, subPath, Accept-Language header detection, Nginx and Apache config examples, SSR auto-redirect
i18n — Global Variants	references/i18n/import-global-variants.md	@angular/common/locales/global/*, manual import in main.ts, when automatic vs manual import applies
i18n — Custom IDs	references/i18n/manage-marked-text.md	@@ prefix for stable IDs, trade-offs vs auto-generated IDs, uniqueness requirement
i18n — Example App	references/i18n/example.md	Full working example with fr-CA/en-US, complete app.component.html, app.component.ts, and messages.fr.xlf
Animations — Enter/Leave	references/animations/overview.md	animate.enter/animate.leave (v20 new API), AnimationCallbackEvent, animationComplete(), MAX_ANIMATION_TIMEOUT, testing, legacy compatibility
Animations — CSS	references/animations/css.md	CSS keyframe animations, transitions, @starting-style, state/style toggling, auto-height, staggering, parallel animations, reordering lists, disabling animations, programmatic control via getAnimations()
Animations — Route Transitions	references/animations/route-transitions.md	View Transitions API, withViewTransitions, enableViewTransitions, CSS pseudo-elements ::view-transition-old/new, onViewTransitionCreated, skipTransition, global styles requirement
Drag and Drop	references/drag-drop/overview.md	CDK cdkDrag/cdkDropList, reorderable lists, transfer between lists, cdkDropListGroup, copying items (cdkDropListHasAnchor), drag handles, custom preview/placeholder, axis locking, boundaries, delay, disable, orientation (vertical/horizontal/mixed), sort predicates, CDK_DRAG_CONFIG, scrollable containers

Best Practices

Topic	File	When to read
Style Guide	references/style-guide/style-guide.md	Naming conventions, project structure, inject() preference, component/directive patterns, protected/readonly usage, event handler naming, lifecycle interfaces
Security	references/best-practices/security.md	XSS prevention, sanitization contexts, DomSanitizer/bypassSecurityTrust*, CSP, Trusted Types, AOT compiler security, XSRF/CSRF, XSSI
Accessibility	references/best-practices/accessibility.md	ARIA attribute binding (attr.), Angular Material/CDK a11y tools, native element patterns, focus management after navigation, ariaCurrentWhenActive, @defer accessibility, custom accessible components
Unhandled Errors	references/best-practices/error-handling.md	ErrorHandler, what Angular catches vs. doesn't, async error handling, provideBrowserGlobalErrorListeners(), SSR error listeners, TestBed error rethrowing
Performance — Overview	references/best-practices/performance-overview.md	Change detection fundamentals, overview of performance subtopics and tools
Performance — Zone Pollution	references/best-practices/zone-pollution.md	Zone.js pollution, runOutsideAngular, third-party lib init, re-entering the zone, NgZone.isInAngularZone()
Performance — Slow Computations	references/best-practices/slow-computations.md	Profiling with DevTools, pure pipes, memoization, avoiding repaints in lifecycle hooks
Performance — Skipping Subtrees	references/best-practices/skipping-subtrees.md	OnPush strategy, change detection scenarios, markForCheck, object reference mutations
Performance — Chrome DevTools	references/best-practices/profiling-chrome-devtools.md	enableProfiling(), Angular custom track, color coding, bootstrap/component/CD profiling
Performance — Zoneless	references/best-practices/zoneless.md	provideZonelessChangeDetection, removing ZoneJS, PendingTasks, OnPush compatibility, testing with whenStable()
Keeping Up to Date	references/updates/keeping-up-to-date.md	ng update, ng version, Angular Update Guide, changelog, version support policy

Routing Logic

When a user asks about Angular, follow this decision tree:

1. Identify the primary topic from the user's question
2. Read the matching reference file(s) — multiple may apply (e.g., a form validation question may need both forms.md and components.md)
3. For best practices questions, also read the relevant best practices file alongside the technical reference
4. For architecture/design questions, read style-guide.md + the relevant technical reference(s)
5. Answer using the reference content — cite Angular v20 patterns, APIs, and conventions

Common Multi-File Lookups

User's Task	Read These
Building a form component	forms/overview.md + forms/reactive-forms.md + components/inputs.md + components/outputs.md
Setting up authentication	routing/route-guards.md + http-client/interceptors.md
SSR with hydration	ssr-hydration/ssr.md + ssr-hydration/hydration.md + routing/rendering-strategies.md
Optimizing a slow app	best-practices/performance-overview.md + best-practices/zone-pollution.md + best-practices/slow-computations.md + best-practices/skipping-subtrees.md + signals/overview.md
Writing tests	testing/overview.md + testing/services.md or testing/components-basics.md + testing/components-scenarios.md as needed
Accessible forms	best-practices/accessibility.md + forms/overview.md + forms/form-validation.md
Drag-and-drop list	drag-drop/overview.md + animations/css.md (if animated)
Lazy loading	templates/defer.md (@defer) + routing/define-routes.md (loadComponent)
Security review	best-practices/security.md + http-client/interceptors.md (XSRF)
i18n setup	i18n/overview.md + i18n/add-package.md + i18n/prepare.md + i18n/translation-files.md + i18n/merge.md
i18n deploying/serving	i18n/deploy.md + i18n/import-global-variants.md
i18n custom IDs	i18n/manage-marked-text.md
Updating Angular version	updates/keeping-up-to-date.md
Component lifecycle	components/lifecycle.md
Dynamic/programmatic rendering	components/programmatic-rendering.md
Two-way binding / model inputs	components/inputs.md
Shadow DOM / style isolation	components/styling.md
Child queries / ViewChild	components/queries.md
Web Components / Angular Elements	components/elements.md

Important Notes

• This skill targets Angular v20 — APIs and patterns are specific to this version
• Angular v20 uses standalone components by default (no NgModules for new code)
• The new animate.enter/animate.leave API replaces legacy @angular/animations for new components
• Signals are the recommended reactivity model — prefer over plain properties and RxJS where appropriate
• When in doubt between approaches, prefer: signals > computed > effect > RxJS