Angular Signals vs. Change Detection: The Performance Showdown!

Great question! 🚀 Angular Signals and Change Detection both impact how Angular updates the UI, but they work very differently under the hood. Let’s break it down.

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⚡ Angular Change Detection (Traditional Approach)

Angular uses Zone.js to track async operations (like HTTP requests, timeouts, and event handlers) and triggers Change Detection to update the UI.

How it Works:

• Every component has a ChangeDetector that checks for updates.
• Angular runs a "dirty checking" cycle on component state changes.
• Default strategy (ChangeDetectionStrategy.Default) checks the whole component tree, even if data hasn’t changed.
• OnPush strategy optimizes by only checking when @Input() changes.

Pros:

✅ Works well with existing Angular apps.

✅ Handles async operations automatically.

✅ OnPush improves performance by skipping unnecessary checks.

Cons:

❌ Can be inefficient for large apps with many components.

❌ Unnecessary checks slow down rendering.

❌ Zone.js overhead can impact performance.

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🔥 Angular Signals (Introduced in Angular 16)

Signals are a new reactive primitive that tracks dependencies automatically. Instead of manually managing ChangeDetectorRef or using OnPush, Signals only trigger updates when the specific value changes.

How it Works:

• A Signal (signal()) is a reactive state that notifies only dependent consumers when it changes.
• No need for Zone.js or manual change detection.
• Fine-grained reactivity: Components update only when they depend on a changed value.

Example:

import { signal, computed, effect } from '@angular/core';

export class CounterComponent {
  count = signal(0);
  double = computed(() => this.count() * 2);

  constructor() {
    effect(() => console.log('Count changed:', this.count()));
  }

  increment() {
    this.count.set(this.count() + 1);
  }
}

Pros:

✅ Faster UI updates: Only affected components re-render.

✅ No unnecessary change detection: Angular updates only what’s needed.

✅ No Zone.js required (can work without it).

✅ Simplifies state management: Works like signals in Solid.js.

Cons:

❌ New learning curve for existing Angular devs.

❌ Still experimental (might need future refinements).

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💡 When to Use What?

Feature	Change Detection	Angular Signals
Uses Zone.js?	✅ Yes	❌ No
Works with Existing Code?	✅ Yes	❌ Needs refactoring
Performance	⚡ Can be slow (default)	🚀 Faster, fine-grained updates
Automatic Change Tracking	❌ Needs @Input() or manual triggers	✅ Yes
Granular Re-renders	❌ No	✅ Yes

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🚀 TL;DR

• Use Angular Change Detection for existing projects where Zone.js handles updates.
• Use Angular Signals for high-performance, reactive apps where fine-grained updates matter.