Angular 17 introduced several new features and improvements, including:

1. Signal-based Components – A new way to manage reactivity in components.
2. Control Flow Syntax – Improved syntax for if, for, and switch statements.
3. Deferred Loading (@defer) – Optimized lazy loading of components.
4. Standalone Components – Further improvements in standalone APIs.
5. Performance Enhancements – Faster rendering and execution.
6. Better TypeScript Support – Improvements in type inference and error handling.

Signal-based components introduce a new way of handling state reactivity in Angular. Unlike traditional Observables, Signals:

• Are synchronous and track dependencies automatically.
• Improve performance by reducing unnecessary re-renders.
• Can be used in computed values and effects.
• Provide a simpler alternative to RxJS in many cases.

Example:

import { signal } from '@angular/core';
export class MyComponent {
  count = signal(0);
  
  increment() {
    this.count.set(this.count() + 1);
  }
}

Angular 17 introduced a modernized control flow syntax, replacing directives like *ngIf and *ngFor.

Example of the new syntax:

@if (isLoggedIn) {
  <p>Welcome, User!</p>
} @else {
  <p>Please log in.</p>
}
@for (user of users; track user.id) {
  <li>{{ user.name }}</li>
}

Standalone components eliminate the need for NgModules, making the structure simpler.

Example:

import { Component } from '@angular/core';
@Component({
  standalone: true,
  selector: 'app-hello',
  template: `<h1>Hello Angular 17!</h1>`,
})
export class HelloComponent {}

• Faster Rendering – Thanks to fine-tuned reactivity with signals.
• Lazy Loading with @defer – Reduces initial bundle size.
• Better Change Detection – More efficient updates with signals.
• Improved Code Splitting – Smaller JavaScript bundles.
• Tree-Shaking Improvements – Unused code is removed more effectively.

Follow these steps to migrate to Angular 17:

• Update Angular CLI and Core:

ng update @angular/cli @angular/core

• Refactor to Standalone Components if applicable.
• Use the new Control Flow Syntax for better performance.
• Replace Observables with Signals where suitable.
• Enable Deferred Loading for lazy components.
• Run Tests to ensure compatibility.

The new control flow syntax offers:

• Better Performance – Directly optimized by the Angular compiler.
• Improved Readability – More like JavaScript’s native syntax.
• Scoped Variables – Works seamlessly with inline conditions.
• No More Structural Directives – Reduces directive complexity.

Example:

@if (user.isAdmin) {
  <p>Admin Panel</p>
} @else {
  <p>Regular User</p>
}

The @defer directive delays rendering of elements until needed, reducing initial page load time.

Examples of usage:

On Viewport (lazy load when visible):

@defer (on viewport) { <img src="large-image.jpg" /> }

On Interaction (load on click):

<button (click)="showContent = true">Load Content</button>
@defer (when showContent) { <p>Loaded on demand!</p> }

This improves performance by reducing unnecessary DOM rendering.

Angular 17 introduced @defer, which allows delayed loading of content. It works alongside:

• @placeholder – Displays temporary content while loading.
• @loading – Shows content when the deferred block is loading.

Example:

@defer (on viewport) {
  <p>Loaded Content</p>
} @placeholder {
  <p>Placeholder while waiting...</p>
} @loading {
  <p>Loading in progress...</p>
}

This enhances performance and user experience.

Angular 17 introduces provideHttpClient(), which simplifies setting up HTTP services without HttpClientModule.

import { provideHttpClient, withInterceptors } from '@angular/common/http';
bootstrapApplication(AppComponent, {
  providers: [provideHttpClient(withInterceptors([myInterceptor]))]
});

Benefits:

• Eliminates the need for NgModule-based imports.
• Supports interceptors inline.
• Works seamlessly with Standalone Components.

Instead of importing RouterModule, use provideRouter() for simpler routing.

Example:

import { provideRouter } from '@angular/router';
bootstrapApplication(AppComponent, {
  providers: [provideRouter([
    { path: '', component: HomeComponent },
    { path: 'about', component: AboutComponent }
  ])]
});

Advantages:

• No need for RouterModule.forRoot().
• Easier tree-shaking and smaller bundle sizes.

Angular 17 introduces provideForms() to replace FormsModule and ReactiveFormsModule.

import { provideForms } from '@angular/forms';
bootstrapApplication(AppComponent, {
  providers: [provideForms()]
});

Use provideHttpClient() with interceptors for HTTP requests.

import { HttpInterceptorFn } from '@angular/common/http';
export const authInterceptor: HttpInterceptorFn = (req, next) => {
  const cloned = req.clone({ setHeaders: { Authorization: 'Bearer token' } });
  return next(cloned);
};
bootstrapApplication(AppComponent, {
  providers: [provideHttpClient(withInterceptors([authInterceptor]))]
});

This simplifies interceptor registration.

It allows enabling animations without importing BrowserAnimationsModule.

Example:

import { provideAnimations } from '@angular/platform-browser/animations';
bootstrapApplication(AppComponent, {
  providers: [provideAnimations()]
});

Benefits:

• Easier setup for animations.
• Improves SSR performance.

Standalone directives work without NgModule.

Example:

import { Directive, ElementRef, Renderer2 } from '@angular/core';
@Directive({
  standalone: true,
  selector: '[appHighlight]'
})
export class HighlightDirective {
  constructor(el: ElementRef, renderer: Renderer2) {
    renderer.setStyle(el.nativeElement, 'backgroundColor', 'yellow');
  }
}

<p appHighlight>Highlighted Text</p>

Standalone Components remove the dependency on NgModule, simplifying development.

Advantages:

• Faster Bootstrapping – No need for module initialization.
• Better Tree-Shaking – Smaller bundle sizes.
• Simplified Dependency Injection – Direct imports without NgModule.
• Easier Lazy Loading – Load standalone components directly.

Example:

@Component({
  standalone: true,
  selector: 'app-hello',
  template: `<h1>Hello Angular 17!</h1>`,
})
export class HelloComponent {}

The new @switch directive replaces *ngSwitch for better readability and performance.

@switch (status) {
  @case ('active') { <p>Active User</p> }
  @case ('inactive') { <p>Inactive User</p> }
  @default { <p>Unknown Status</p> }
}

Advantages:

• More readable and closer to JavaScript’s switch-case syntax.
• No need for multiple *ngSwitchCase directives.

Angular 17 simplifies DI with:

• Standalone Components – Directly declare dependencies without modules.
• Functional Providers – Use provideX() for services and features.
• Tree-Shakable Providers – Unused services are removed from bundles.
• Example of providing a service in a Standalone Component:

@Component({
  standalone: true,
  selector: 'app-user',
  template: `<p>User Component</p>`,
  providers: [UserService] 
})
export class UserComponent {}

Angular 17 introduces Signal-based reactivity, which reduces unnecessary change detection cycles.

Key improvements:

• Automatic Dependency Tracking – Components re-render only when needed.
• No Need for @Input and @Output – Use Signals instead.
• Better Performance with Fine-Grained Updates – Avoids detecting changes in the entire component tree.

Example using Signals:

import { signal } from '@angular/core';
@Component({
  selector: 'app-profile',
  template: `<p>Name: {{ name() }}</p>`
})
export class ProfileComponent {
  name = signal('Alice');
  updateName() {
    this.name.set('Bob'); // Only this property updates
  }
}

Use @defer with strategies to control how and when a component loads.

Examples:

On User Interaction:

<button (click)="load = true">Load Content</button>
@defer (when load) {
  <p>Loaded on demand</p>
}

@defer (on idle) {
  <p>Loaded in the background</p>
}

@defer (after 5s) {
  <p>Loaded after 5 seconds</p>
}

Angular 17 uses functional route guards instead of class-based guards.

Example of a functional canActivate guard:

import { inject } from '@angular/core';
import { CanActivateFn } from '@angular/router';
import { AuthService } from './auth.service';
export const authGuard: CanActivateFn = (route, state) => {
  const authService = inject(AuthService);
  return authService.isLoggedIn();
};

Benefits:

• Simpler syntax – Uses functions instead of classes.
• Easier testing – No need for DI in a separate class.

Functional interceptors simplify HTTP request handling.

import { HttpInterceptorFn } from '@angular/common/http';
export const authInterceptor: HttpInterceptorFn = (req, next) => {
  const cloned = req.clone({ setHeaders: { Authorization: 'Bearer token' } });
  return next(cloned);
};

Benefits:

• Simpler syntax – No need for class-based interceptors.
• Easier to register – Use provideHttpClient().

Signals simplify state management with automatic reactivity.

import { signal } from '@angular/core';
@Component({
  selector: 'app-counter',
  template: `<button (click)="increment()">Count: {{ count() }}</button>`
})
export class CounterComponent {
  count = signal(0);
  increment() {
    this.count.set(this.count() + 1);
  }
}

Benefits:

• Eliminates the need for RxJS in simple cases.
• Automatic dependency tracking.

Best practices for Angular 17 performance optimization:

• Use @defer – Lazy load components when needed.
• Switch to Signals – Reduce change detection overhead.
• Use Standalone Components – Eliminate unnecessary NgModules.
• Optimize Change Detection – Use OnPush strategy where applicable.
• Use provideHttpClient() – Improve tree-shaking in HTTP requests.
• Enable SSR Hydration – Reduce re-renders in server-side apps.

Angular 17 improves CLI commands for a better developer experience:

1. Faster Builds – Optimized compilation speed.
2. Improved Code Splitting – Better chunk management.
3. New Standalone Project Templates – ng new now supports standalone components by default.

ng new my-app --standalone

provideEffects() allows standalone registration of NgRx effects without needing a module.

import { provideEffects } from '@ngrx/effects';
import { UserEffects } from './user.effects';
bootstrapApplication(AppComponent, {
  providers: [provideEffects(UserEffects)]
});

Benefits:

• Removes dependency on EffectsModule.
• Optimized Tree-Shaking – Only includes necessary effects.

Angular 17 integrates View Transitions API for smoother page transitions.

Example:

import { enableViewTransitions } from '@angular/core';
bootstrapApplication(AppComponent, {
  providers: [enableViewTransitions()]
});

Usage in a component:

<button (click)="navigate()">Navigate</button>

navigate() {
  document.startViewTransition(() => this.router.navigate(['/new-page']));
}

Benefits:

• Native-like smooth transitions.
• No third-party animation libraries needed.

Route Signals provide a reactive approach to reading route parameters and query params.

Example:

import { inject } from '@angular/core';
import { signal } from '@angular/core';
import { ActivatedRoute } from '@angular/router';
export class ProductComponent {
  route = inject(ActivatedRoute);
  productId = signal(this.route.snapshot.paramMap.get('id'));
}

Advantages:

• Replaces BehaviorSubject and Observable patterns.
• More efficient than ActivatedRoute subscriptions.

Angular 17 improves lazy loading of translations and efficient message extraction.

New i18n features:

• Better runtime translations – Supports @defer for language-specific content.
• Standalone API for translations – No need for modules.
• More compact locale data – Reduces bundle size.

Example:

<p>{{ 'HELLO' | translate }}</p>

import { provideI18n } from '@angular/core';
bootstrapApplication(AppComponent, {
  providers: [provideI18n({ defaultLocale: 'en' })]
});

Angular 17 introduces:

• provideForms() – Replaces FormsModule and ReactiveFormsModule.
• Built-in validation signals – Easier form state management.
• Optimized performance – Faster reactivity with Signals.

Example:

import { provideForms, FormControl } from '@angular/forms';
@Component({
  selector: 'app-login',
  template: `<input [formControl]="email" />`
})
export class LoginComponent {
  email = new FormControl('');
}

Angular 17 allows creating projects without NgModules:

ng new my-app --standalone

Advantages:

• Faster application startup.
• Simplified project structure.
• Better Tree-Shaking – No unnecessary modules.

Functional resolvers replace class-based resolvers for fetching data before navigation.

import { ResolveFn } from '@angular/router';
export const productResolver: ResolveFn<Product> = (route) => {
  return fetch(`/api/products/${route.paramMap.get('id')}`).then(res => res.json());
};

Advantages:

• Simpler than class-based resolvers.
• No need for dependency injection.