angular-signals
ALWAYS use when working with Angular Signals, signal-based reactivity, computed signals, or effect APIs in Angular applications.
What this skill does
# Angular Signals
**Version:** Angular 16+ (2025)
**Tags:** Reactivity, State Management, Signals API
**References:** [Angular Signals](https://angular.dev/guide/signals) • [API Reference](https://angular.dev/api/core)
## API Changes
This section documents version-specific API changes.
- NEW: Angular 19 Resource API — New way to handle async data with built-in loading/error states
- NEW: linkedSignal() — Creates a signal linked to external sources with getter/setter [source](https://sagarsnath.medium.com/deep-dive-into-computed-effect-and-linkedsignal-in-angular-signals)
- NEW: Signal inputs — Use `input()` and `input.required()` for reactive component inputs
- NEW: `toSignal()` and `toObservable()` — Bridge between RxJS and Signals
- NEW: `effect()` improvements — Better cleanup with `onCleanup` callback
- NEW: Zoneless change detection — Works seamlessly with Signals
## Best Practices
- Use `computed()` for derived state — Never use `effect()` for deriving values
```ts
// ✅ DO THIS - derived state
totalPrice = computed(() => {
return this.items().reduce((sum, item) => sum + item.price, 0);
});
// ❌ DON'T - side effects in computed
badComputed = computed(() => {
const data = this.data();
this.logService.log(data); // Side effect - don't do this!
});
```
- Use `signal()` for writable state
```ts
count = signal(0);
// Update with set()
count.set(5);
// Update with update()
count.update(value => value + 1);
// Update with mutate() for objects
user.update(u => ({ ...u, name: 'New Name' }));
```
- Use `effect()` only for side effects
```ts
effect(() => {
analytics.track('cart-updated', {
itemCount: this.items().length
});
});
```
- Always cleanup effects to prevent memory leaks
```ts
effect((onCleanup) => {
const timer = setTimeout(() => { /* ... */ }, 300);
onCleanup(() => clearTimeout(timer));
});
```
- Use Signal Inputs instead of traditional @Input()
```ts
// Modern signal inputs (Angular 17+)
userId = input<string>('');
user = input.required<User>();
// Computed based on input
greeting = computed(() => `Hello, ${this.user()?.name}`);
```
- Use `toSignal()` for RxJS to Signal conversion
```ts
// Convert Observable to Signal
users = toSignal(this.http.get('/api/users'), { initialValue: [] });
```
- Don't nest effects — Can cause performance issues
- Use equality functions for complex object comparisons
```ts
user = signal<User | null>(null, {
equal: (a, b) => a?.id === b?.id
});
```
- Use Signals for UI state, RxJS for complex async — Signals and RxJS serve different purposes
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