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What does linkedSignal do?
Angular’s linkedSignal creates a writable signal whose initial value and subsequent resets come from a reactive computation. It sits between two common needs: signal stores independent writable state, while computed exposes a read-only value derived from other signals.
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The API reference marks linkedSignal stable since Angular v20.0. Check the Angular version installed in your project and the matching API documentation before adopting it, because the current syntax and availability depend on that version.
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Use it when a derived value needs to be temporarily or directly changed by application code, yet should be recalculated when its dependencies change. For example, a notification preference might default to enabled when a user is online while still allowing the user to disable notifications manually.
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import { linkedSignal, signal } from '@angular/core';
const userStatus = signal<'online' | 'away' | 'offline'>('offline');
const notificationsEnabled = linkedSignal(() => userStatus() === 'online');
notificationsEnabled.set(true); // A manual override is allowed.
userStatus.set('online'); // A dependency change can re-sync the value.Here, notificationsEnabled is writable, unlike a computed signal. When the linked computation runs because its dependency changes, it supplies the linked value again. Choose this model when that re-synchronization is the intended behavior.
How do you keep a selection valid when its options change?
The source-and-computation overload is useful when a derived choice depends on a changing collection. If a user selected an option and the available options change, always choosing the first item can discard a selection that remains valid. The computation can inspect the new source and the previous source and linked value, then retain the old choice if it is still available or choose a valid fallback.
linkedSignal({
source: options,
computation: (newOptions, previous) => {
const previousChoice = previous?.value;
return previousChoice && newOptions.includes(previousChoice)
? previousChoice
: newOptions[0];
},
});This illustrates the decision, not a complete component: define the option types and handle an empty list according to the application’s requirements. In this overload, the computation receives the new source and a previous object containing the previous source and linked value.
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Angular’s guide also documents custom equality comparison and an optional custom set operation. A custom setter can route writes back to a source of truth; use it deliberately so it remains clear which part of the application owns the state.
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Should you use signal, computed, linkedSignal, or effect?
| Need | Use | Why |
|---|---|---|
| Independent state that application code writes | signal |
Stores a writable value without deriving it from other signals. |
| A value always derived from dependencies and never manually changed | computed |
Provides a read-only derived value. |
| A value derived from dependencies that must also be writable | linkedSignal |
Allows writes while remaining reactively linked; its computation supplies the value when linked dependencies change. |
| Synchronization with an imperative API or another non-signal system | effect |
Effects are intended for side effects, not for copying derived signal state. |
For read-only derivation, prefer computed. For writable derived state, use linkedSignal. Angular recommends effects for synchronizing with imperative APIs and other side effects rather than mirroring one signal into another.
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What should you check before adopting it?
- Confirm the project’s Angular version and verify the API against documentation for that release.
- Decide what should happen to a manual override when linked dependencies change; the computation will supply the value again.
- For changing collections, decide explicitly whether a previous choice remains valid and what fallback to use if it does not.
- Keep state ownership clear if using a custom setter to route writes elsewhere.
- Do not use an effect solely to copy a derived value when
computedorlinkedSignalexpresses the relationship directly.
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