# Angular 18: Signals and New Features

> Discover Angular 18 Signals, zoneless change detection, and new signal-based APIs to build more performant applications.

- Published: 2026-01-18
- Updated: 2026-03-31
- Author: SharpSkill
- Tags: angular 18, angular signals, zoneless, signal inputs, reactivity
- Reading time: 12 min

---

Angular 18 marks a turning point in the framework's evolution with the stabilization of Signals. This new reactive primitive fundamentally transforms how Angular components are built, offering a modern alternative to traditional decorators while paving the way for Zone.js-free change detection.

> **What you will learn**
>
> Angular 18's signal-based APIs: input(), model(), viewChild(), and zoneless configuration for lighter and more performant applications.

## Understanding Signals in Angular 18

Signals represent a new approach to reactivity in Angular. Unlike classic decorators like `@Input()` that rely on Zone.js change detection, Signals offer fine-grained and explicit reactivity. Each Signal encapsulates a value and automatically notifies consumers when that value changes.

This approach offers several advantages: better performance through targeted updates, native integration with `computed()` and `effect()` functions, and preparation for Angular's zoneless future.

```typescript
// signals-basics.component.ts
// Demonstration of fundamental Signal concepts
import { Component, signal, computed, effect } from '@angular/core';

@Component({
  selector: 'app-counter',
  standalone: true,
  template: `
    <div class="counter-container">
      <h2>Counter: {{ count() }}</h2>
      <p>Double: {{ doubleCount() }}</p>

      <button (click)="increment()">+1</button>
      <button (click)="decrement()">-1</button>
      <button (click)="reset()">Reset</button>
    </div>
  `
})
export class CounterComponent {
  // Writable signal - value can be modified
  count = signal(0);

  // Computed signal - automatically derived from count
  // Only recalculates when count changes
  doubleCount = computed(() => this.count() * 2);

  constructor() {
    // Effect - executed on every count change
    // Useful for side effects (logs, API calls, etc.)
    effect(() => {
      console.log(`New counter value: ${this.count()}`);
    });
  }

  increment() {
    // update() allows modification based on previous value
    this.count.update(value => value + 1);
  }

  decrement() {
    this.count.update(value => value - 1);
  }

  reset() {
    // set() directly replaces the value
    this.count.set(0);
  }
}
```

Signals work as reactive containers: `signal()` creates a writable Signal, `computed()` derives calculated values, and `effect()` allows executing actions in response to changes.

## Signal Inputs with input()

The `input()` function replaces the traditional `@Input()` decorator. It returns a read-only `InputSignal`, ensuring that data always flows from parent to child without accidental modification.

```typescript
// book-card.component.ts
// Component using signal inputs
import { Component, input, computed } from '@angular/core';

interface Book {
  id: string;
  title: string;
  author: string;
  price: number;
  discountPercent?: number;
}

@Component({
  selector: 'app-book-card',
  standalone: true,
  template: `
    <article class="book-card">
      <h3>{{ book().title }}</h3>
      <p class="author">By {{ book().author }}</p>

      @if (hasDiscount()) {
        <p class="price">
          <span class="original">\${{ book().price }}</span>
          <span class="discounted">\${{ discountedPrice() }}</span>
        </p>
      } @else {
        <p class="price">\${{ book().price }}</p>
      }

      @if (featured()) {
        <span class="badge">Featured</span>
      }
    </article>
  `
})
export class BookCardComponent {
  // Required input - template won't compile without this prop
  book = input.required<Book>();

  // Optional input with default value
  featured = input(false);

  // Computed based on input - automatically recalculated
  hasDiscount = computed(() => {
    const discount = this.book().discountPercent;
    return discount !== undefined && discount > 0;
  });

  // Discounted price calculation
  discountedPrice = computed(() => {
    const { price, discountPercent } = this.book();
    if (!discountPercent) return price;
    return (price * (100 - discountPercent) / 100).toFixed(2);
  });
}
```

Usage in a parent template remains similar, but with type safety and Signal reactivity:

```typescript
// book-list.component.ts
// Parent component using book-card
import { Component, signal } from '@angular/core';
import { BookCardComponent } from './book-card.component';

@Component({
  selector: 'app-book-list',
  standalone: true,
  imports: [BookCardComponent],
  template: `
    <div class="book-grid">
      @for (book of books(); track book.id) {
        <app-book-card
          [book]="book"
          [featured]="book.id === featuredBookId()"
        />
      }
    </div>
  `
})
export class BookListComponent {
  books = signal<Book[]>([
    { id: '1', title: 'Clean Code', author: 'Robert C. Martin', price: 35 },
    { id: '2', title: 'The Pragmatic Programmer', author: 'David Thomas', price: 42, discountPercent: 15 }
  ]);

  featuredBookId = signal('1');
}
```

The major difference from `@Input()`: signal inputs are read-only. Calling `this.book.set()` from the child component is impossible, which reinforces unidirectional data flow.

## Two-Way Binding with model()

For cases requiring bidirectional synchronization, Angular 18 introduces `model()`. This function creates a writable Signal that automatically propagates changes to the parent component.

```typescript
// search-input.component.ts
// Component with bidirectional binding via model()
import { Component, model, output, computed } from '@angular/core';

@Component({
  selector: 'app-search-input',
  standalone: true,
  template: `
    <div class="search-container">
      <input
        type="text"
        [value]="query()"
        (input)="onInput($event)"
        [placeholder]="placeholder()"
        class="search-input"
      />

      @if (query().length > 0) {
        <button (click)="clear()" class="clear-btn">×</button>
      }

      <span class="char-count">{{ charCount() }} characters</span>
    </div>
  `
})
export class SearchInputComponent {
  // model() creates a bidirectional Signal
  // Modifications propagate to parent
  query = model('');

  // Classic input for configuration
  placeholder = model('Search...');

  // Output for additional events
  searchSubmitted = output<string>();

  // Computed based on model
  charCount = computed(() => this.query().length);

  onInput(event: Event) {
    const value = (event.target as HTMLInputElement).value;
    // Update model - propagates to parent
    this.query.set(value);
  }

  clear() {
    this.query.set('');
  }

  submit() {
    if (this.query().length > 0) {
      this.searchSubmitted.emit(this.query());
    }
  }
}
```

The parent uses the banana-in-a-box syntax `[()]` for bidirectional binding:

```typescript
// app.component.ts
// Using two-way binding with model()
import { Component, signal, effect } from '@angular/core';
import { SearchInputComponent } from './search-input.component';

@Component({
  selector: 'app-root',
  standalone: true,
  imports: [SearchInputComponent],
  template: `
    <div class="app-container">
      <app-search-input [(query)]="searchTerm" />

      <p>Current search: {{ searchTerm() }}</p>

      <div class="results">
        @for (result of filteredResults(); track result.id) {
          <div class="result-item">{{ result.name }}</div>
        }
      </div>
    </div>
  `
})
export class AppComponent {
  // Local signal synchronized with child component
  searchTerm = signal('');

  results = signal([
    { id: 1, name: 'Angular 18' },
    { id: 2, name: 'React 19' },
    { id: 3, name: 'Vue 3' }
  ]);

  // Reactive filtering based on searchTerm
  filteredResults = computed(() => {
    const term = this.searchTerm().toLowerCase();
    if (!term) return this.results();
    return this.results().filter(r =>
      r.name.toLowerCase().includes(term)
    );
  });
}
```

> **model() vs input()**
>
> Use `input()` for read-only data (parent → child). Use `model()` when the child component needs to modify the value (bidirectional).

## Signal Queries with viewChild() and contentChild()

The `viewChild()`, `viewChildren()`, `contentChild()`, and `contentChildren()` functions replace their corresponding decorators. They return Signals, eliminating the need for lifecycle hooks like `ngAfterViewInit`.

```typescript
// form-container.component.ts
// Demonstration of signal queries
import {
  Component,
  viewChild,
  viewChildren,
  ElementRef,
  effect,
  signal
} from '@angular/core';
import { FormFieldComponent } from './form-field.component';

@Component({
  selector: 'app-form-container',
  standalone: true,
  imports: [FormFieldComponent],
  template: `
    <form #formElement (submit)="onSubmit($event)">
      <input #firstInput type="text" placeholder="Name" />

      <app-form-field label="Email" />
      <app-form-field label="Phone" />

      <div class="actions">
        <button type="submit">Submit</button>
        <button type="button" (click)="focusFirst()">Focus first field</button>
      </div>
    </form>
  `
})
export class FormContainerComponent {
  // viewChild returns Signal<ElementRef | undefined>
  formElement = viewChild<ElementRef>('formElement');

  // viewChild.required guarantees element exists
  firstInput = viewChild.required<ElementRef<HTMLInputElement>>('firstInput');

  // Query on a component - returns the component itself
  firstFormField = viewChild(FormFieldComponent);

  // viewChildren for multiple elements
  allFormFields = viewChildren(FormFieldComponent);

  constructor() {
    // Effect replaces ngAfterViewInit for queries
    effect(() => {
      // Signal is automatically resolved
      const input = this.firstInput();
      console.log('First input available:', input.nativeElement);
    });

    // React to list changes
    effect(() => {
      const fields = this.allFormFields();
      console.log(`${fields.length} form fields found`);
    });
  }

  focusFirst() {
    // Direct access via Signal
    this.firstInput().nativeElement.focus();
  }

  onSubmit(event: Event) {
    event.preventDefault();
    // Access the form
    const form = this.formElement();
    if (form) {
      console.log('Form submitted');
    }
  }
}
```

For projecting content and accessing it, `contentChild()` works similarly:

```typescript
// card.component.ts
// Using contentChild for projected content
import { Component, contentChild, contentChildren, TemplateRef } from '@angular/core';

@Component({
  selector: 'app-card',
  standalone: true,
  template: `
    <div class="card">
      <header class="card-header">
        <ng-content select="[card-title]" />
      </header>

      <div class="card-body">
        <ng-content />
      </div>

      @if (hasFooter()) {
        <footer class="card-footer">
          <ng-content select="[card-footer]" />
        </footer>
      }
    </div>
  `
})
export class CardComponent {
  // Detect if footer was projected
  footerContent = contentChild<ElementRef>('[card-footer]');

  // Computed to check footer presence
  hasFooter = computed(() => this.footerContent() !== undefined);
}
```

## Zoneless Change Detection

Angular 18 introduces Zone.js-free change detection in experimental mode. This feature reduces bundle size by approximately 13 KB and improves performance by eliminating monkey-patches on browser async APIs.

```typescript
// main.ts
// Configuring the application in zoneless mode
import { bootstrapApplication } from '@angular/platform-browser';
import { provideExperimentalZonelessChangeDetection } from '@angular/core';
import { AppComponent } from './app/app.component';

bootstrapApplication(AppComponent, {
  providers: [
    // Enable experimental zoneless detection
    provideExperimentalZonelessChangeDetection()
  ]
});
```

The `angular.json` configuration must also be updated to remove Zone.js:

```json
{
  "projects": {
    "my-app": {
      "architect": {
        "build": {
          "options": {
            "polyfills": []
          }
        }
      }
    }
  }
}
```

In zoneless mode, change detection triggers automatically in these cases: Signal update, `markForCheck()` call, new value received via AsyncPipe, or component attach/detach.

```typescript
// zoneless-counter.component.ts
// Component optimized for zoneless mode
import {
  Component,
  signal,
  ChangeDetectionStrategy,
  inject
} from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { toSignal } from '@angular/core/rxjs-interop';

@Component({
  selector: 'app-zoneless-counter',
  standalone: true,
  // OnPush recommended for zoneless
  changeDetection: ChangeDetectionStrategy.OnPush,
  template: `
    <div class="counter">
      <p>Counter: {{ count() }}</p>
      <button (click)="increment()">Increment</button>

      @if (loading()) {
        <p>Loading...</p>
      }

      @if (data()) {
        <pre>{{ data() | json }}</pre>
      }
    </div>
  `
})
export class ZonelessCounterComponent {
  private http = inject(HttpClient);

  count = signal(0);
  loading = signal(false);
  data = signal<any>(null);

  increment() {
    // Signal update triggers detection
    this.count.update(c => c + 1);
  }

  async fetchData() {
    this.loading.set(true);

    try {
      // Signals guarantee view updates
      const response = await fetch('/api/data');
      const json = await response.json();
      this.data.set(json);
    } finally {
      this.loading.set(false);
    }
  }
}
```

> **Zoneless Compatibility**
>
> Components using `ChangeDetectionStrategy.OnPush` and Signals are generally compatible with zoneless mode. Avoid direct modifications of properties that are not Signals.

## Migrating Existing Components

Migration to signal-based APIs can be done gradually. Here's an example of refactoring a traditional component:

```typescript
// BEFORE: Component with classic decorators
// user-profile-legacy.component.ts
import { Component, Input, ViewChild, ElementRef, AfterViewInit } from '@angular/core';

@Component({
  selector: 'app-user-profile-legacy',
  template: `
    <div #container>
      <h2>{{ user.name }}</h2>
      <p>{{ user.email }}</p>
    </div>
  `
})
export class UserProfileLegacyComponent implements AfterViewInit {
  @Input() user!: { name: string; email: string };
  @ViewChild('container') container!: ElementRef;

  ngAfterViewInit() {
    console.log('Container ready:', this.container.nativeElement);
  }
}
```

```typescript
// AFTER: Component migrated to Signals
// user-profile.component.ts
import { Component, input, viewChild, ElementRef, effect } from '@angular/core';

interface User {
  name: string;
  email: string;
}

@Component({
  selector: 'app-user-profile',
  standalone: true,
  template: `
    <div #container>
      <h2>{{ user().name }}</h2>
      <p>{{ user().email }}</p>
    </div>
  `
})
export class UserProfileComponent {
  // input.required replaces @Input() with !
  user = input.required<User>();

  // viewChild.required replaces @ViewChild with !
  container = viewChild.required<ElementRef>('container');

  constructor() {
    // effect replaces ngAfterViewInit for queries
    effect(() => {
      console.log('Container ready:', this.container().nativeElement);
    });
  }
}
```

Benefits of this migration: stricter typing, automatic reactivity, less boilerplate code, and zoneless mode compatibility.

## Best Practices with Signals

Key recommendations to get the most out of Signals in Angular 18:

```typescript
// best-practices.component.ts
// Example of best practices with Signals
import {
  Component,
  signal,
  computed,
  effect,
  untracked,
  ChangeDetectionStrategy
} from '@angular/core';

interface Product {
  id: string;
  name: string;
  price: number;
  quantity: number;
}

@Component({
  selector: 'app-cart',
  standalone: true,
  changeDetection: ChangeDetectionStrategy.OnPush,
  template: `
    <div class="cart">
      <h2>Cart ({{ itemCount() }} items)</h2>

      @for (item of items(); track item.id) {
        <div class="cart-item">
          <span>{{ item.name }}</span>
          <span>{{ item.quantity }} × \${{ item.price }}</span>
          <button (click)="removeItem(item.id)">Remove</button>
        </div>
      }

      <div class="cart-total">
        <strong>Total: \${{ total() }}</strong>
      </div>
    </div>
  `
})
export class CartComponent {
  // Signal for mutable data
  items = signal<Product[]>([]);

  // Computed for derived values - avoids unnecessary recalculations
  itemCount = computed(() => this.items().length);

  total = computed(() =>
    this.items().reduce((sum, item) => sum + item.price * item.quantity, 0)
  );

  constructor() {
    // Effect for side effects (analytics, persistence)
    effect(() => {
      const currentItems = this.items();
      // untracked avoids creating a dependency
      untracked(() => {
        localStorage.setItem('cart', JSON.stringify(currentItems));
      });
    });
  }

  addItem(product: Product) {
    // update() for modifications based on previous state
    this.items.update(current => {
      const existing = current.find(i => i.id === product.id);
      if (existing) {
        return current.map(i =>
          i.id === product.id
            ? { ...i, quantity: i.quantity + 1 }
            : i
        );
      }
      return [...current, { ...product, quantity: 1 }];
    });
  }

  removeItem(id: string) {
    this.items.update(current => current.filter(i => i.id !== id));
  }
}
```

Key points to remember:

- Use `computed()` for derived values rather than recalculating in the template
- Prefer `update()` over `set()` when the new value depends on the old one
- Use `untracked()` in effects to avoid circular dependencies
- Always specify `track` in `@for` loops to optimize rendering

## Conclusion

Angular 18 lays the foundation for a Zone.js-free future through Signals. Key takeaways:

- ✅ **input()** replaces `@Input()` with stricter typing and guaranteed read-only access
- ✅ **model()** enables reactive two-way binding between parent and child
- ✅ **viewChild()** and **contentChild()** eliminate the need for lifecycle hooks
- ✅ **Zoneless** reduces bundle size and improves performance
- ✅ **computed()** and **effect()** complete the reactive ecosystem
- ✅ Gradual migration is possible component by component

Adopting Signals prepares Angular applications for future versions where zoneless mode will become the norm. This transition represents a wise investment for long-term maintainability and performance.

---

Source: SharpSkill (https://sharpskill.dev), tech interview preparation for your real stack.
HTML version of this page: https://sharpskill.dev/en/blog/angular/angular-18-signals-new-features