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Angular

Angular cheat sheet covering components, services, RxJS, dependency injection, routing, and TypeScript patterns with code examples.

18 min read
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Setup & CLI

Angular installation and CLI commands

Installation & Setup

Setting up Angular development environment

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💡 Use ng new with --strict for stricter TypeScript settings
⚡ ng serve automatically reloads on file changes
📌 Production builds include tree-shaking and minification
🔥 Use ng update to keep Angular versions in sync

Angular CLI Commands

Essential Angular CLI commands for development

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💡 Use --dry-run flag to preview changes without creating files
⚡ Shortcuts: g (generate), c (component), s (service), m (module)
📌 Use --skip-tests to skip test file generation
🔥 Standalone components don't need module declarations

Components

Angular components and lifecycle

Component Basics

Standalone components are the default in Angular 17+. NgModule is legacy.

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💡 Standalone is the default in Angular 17+ — no AppModule needed
⚡ Import dependencies directly in the component's `imports` array
📌 Bootstrap with bootstrapApplication() + provideX() helpers
🔥 ng generate @angular/core:standalone migrates legacy NgModule apps

Component Communication

Input, Output, and component interaction

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💡 Use @Input for data flow down, @Output for events up
⚡ ViewChild is resolved after ngAfterViewInit
📌 Two-way binding uses pattern: [(prop)]="value"
🔥 Content projection allows flexible component composition

ViewChild & ContentChild

Accessing child components and elements

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💡 Use static: true for ViewChild if you need it in ngOnInit
⚡ ViewChildren returns a QueryList that updates automatically
📌 ContentChild queries projected content from ng-content
🔥 Access child components after ngAfterViewInit lifecycle hook

Lifecycle Hooks

Component lifecycle methods

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💡 Use ngOnInit for initialization, not constructor
⚡ Always unsubscribe in ngOnDestroy to prevent memory leaks
📌 ngAfterViewInit is safe for DOM manipulation
🔥 Avoid heavy operations in frequently called hooks

Templates & Directives

Template syntax and built-in directives

Template Syntax

Data binding and template expressions

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💡 Use safe navigation (?) to avoid null reference errors
⚡ Prefer property binding [prop] over string interpolation
📌 Template reference variables provide direct access to elements
🔥 ng-container groups elements without adding DOM nodes

Control Flow (@if / @for / @switch)

Built-in template control flow — replaces *ngIf/*ngFor/*ngSwitch in Angular 17+.

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💡 @if/@for/@switch are the modern way (Angular 17+) — no imports needed
⚠️ @for REQUIRES a track expression — usually track item.id or track $index
⚡ @for $index/$first/$last/$even/$odd are available as local variables
🔥 ng generate @angular/core:control-flow migrates *ngIf/*ngFor/*ngSwitch

Deferrable Views (@defer)

Lazy-load template chunks with @defer blocks (Angular 17+).

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💡 @defer auto-code-splits its block into a separate chunk
⚡ on viewport + prefetch on idle is the most common pattern for below-the-fold widgets
📌 @placeholder/@loading/@error are all optional but recommended for UX
🔥 minimum X prevents flicker when content loads faster than the placeholder

Services & DI

Services and dependency injection

Services

Creating and using Angular services

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💡 Use providedIn: 'root' for singleton services
⚡ Handle errors gracefully with catchError
📌 BehaviorSubject for state management
🔥 Always unsubscribe to prevent memory leaks

Dependency Injection

DI patterns and providers

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💡 Use InjectionToken for non-class dependencies
⚡ providedIn: 'root' enables tree-shaking
📌 Hierarchical DI allows different instances at different levels
🔥 Use factories for complex initialization logic

Routing

Angular router configuration and navigation

Route Configuration

Setting up routes and navigation

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💡 Use lazy loading for large feature modules
⚡ PreloadAllModules strategy improves perceived performance
📌 Order matters - wildcard route must be last
🔥 Use routerLinkActive for navigation highlighting

Guards & Resolvers

Route guards and data resolvers

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💡 Use guards to control access to routes
⚡ Resolvers ensure data is loaded before component
📌 Functional guards are simpler for basic checks
🔥 CanDeactivate prevents accidental data loss

Forms

Template-driven and reactive forms

Template-Driven Forms

Forms with ngModel and template validation

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💡 Template-driven forms are simpler for basic forms
⚡ Use template reference variables for validation
📌 ngModelGroup creates nested form groups
🔥 Import FormsModule to use template-driven forms

Reactive Forms

Forms with FormControl and validators

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💡 Reactive forms provide more control and testability
⚡ Use FormBuilder for cleaner syntax
📌 Async validators for server-side validation
🔥 FormArray for dynamic form fields

HTTP & Observables

HTTP client and RxJS observables

HTTP Client

Making HTTP requests with HttpClient

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💡 Always handle errors with catchError operator
⚡ Use interceptors for cross-cutting concerns
📌 Set responseType for non-JSON responses
🔥 Use reportProgress for file upload progress

RxJS Observables

Working with observables and operators

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💡 Use appropriate flattening operator (switchMap for searches)
⚡ takeUntil pattern prevents memory leaks
📌 BehaviorSubject for state management
🔥 shareReplay for caching HTTP requests

Advanced Features

Pipes, directives, and performance

Pipes & Directives

Custom pipes and directives

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💡 Keep pipes pure for better performance
⚡ Use trackBy in ngFor for large lists
📌 Directives add behavior to existing elements
🔥 OnPush change detection optimizes performance

Signals (Angular 16+)

Reactive primitive for state management

Signal Basics

Creating and using signals for reactive state

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💡 Signals provide fine-grained reactivity without Zone.js
⚡ Computed signals are memoized and only recalculate when dependencies change
📌 Effects run automatically when their signal dependencies change
🔥 Use signal inputs for better performance than traditional @Input

Signal Outputs, linkedSignal & Resources

Signal-based outputs and async resources (Angular 17.3+, 19+).

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💡 output() replaces @Output() — type-safe, no EventEmitter import
⚡ linkedSignal is writable but auto-resets when its source changes
📌 resource() turns async data into a signal with isLoading/error/value/reload
🔥 httpResource() (19.2+) is the declarative way to bind HTTP to a signal

Animations

Built-in Angular animation API

Animation Basics

Creating animations with Angular animations API

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💡 Use :enter and :leave for elements being added/removed from DOM
⚡ Stagger animations for lists create smooth sequential effects
📌 Always import BrowserAnimationsModule in your app module
🔥 Use NoopAnimationsModule for testing to disable animations

Testing

Built-in testing with Karma, Jasmine, and TestBed

Component Testing

Testing Angular components with TestBed

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💡 Use TestBed.configureTestingModule to set up test environment
⚡ Mock external dependencies for isolated unit tests
📌 Use fixture.detectChanges() to trigger change detection
🔥 HttpTestingController helps test HTTP requests without actual calls

Performance

Built-in performance optimization features

Performance Optimization

OnPush strategy, trackBy, and lazy loading

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💡 OnPush strategy skips change detection if inputs haven't changed
⚡ Always use trackBy with ngFor for large lists
📌 Lazy load modules to reduce initial bundle size
🔥 Use virtual scrolling for large lists (CDK required)

Security

Built-in security features and sanitization

Security & Sanitization

XSS protection and content sanitization

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💡 Angular automatically sanitizes innerHTML to prevent XSS
⚡ Use DomSanitizer.bypassSecurityTrust* only for trusted content
📌 Always validate and sanitize user input on both client and server
🔥 Implement CSP headers to prevent unauthorized script execution

Accessibility

Built-in accessibility features and ARIA support

Accessibility (A11y)

ARIA attributes and CDK A11y utilities

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💡 Always use semantic HTML elements when possible
⚡ CDK A11y provides utilities for focus management and live announcements
📌 Use ARIA attributes to provide context for screen readers
🔥 Test with keyboard navigation and screen readers

i18n

Built-in internationalization support

Internationalization (i18n)

Built-in i18n for multi-language support

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💡 Use i18n attribute to mark text for translation
⚡ Angular CLI extracts and manages translation files automatically
📌 Build separate bundles for each locale for best performance
🔥 Use ICU message format for complex pluralization and selection