Angular: NG0600: Writing to signals is not allowed in a computed or an effect by default
A computed() (or, by default, an effect()) tried to call .set() or .update() on a signal — that creates hidden update loops.
NG0600: Writing to signals is not allowedWriting to signals is not allowed in a `computed`Writing to signals is not allowed in a `computed` or an `effect` by default Meaning
computed must be a pure derivation. Effects used to forbid signal writes unless allowSignalWrites: true (since Angular 19 writes in effects are allowed). Move the write to an event handler, derive the value with computed instead, or use linkedSignal / toObservable where appropriate.
Common causes
- Calling
.set()/.update()insidecomputed(() => ...) - Writing to a signal inside an
effect()withoutallowSignalWrites(Angular 16–18) - Template function that writes to a signal during render
- Using effects to sync two signals that should be derived
⚡ Quick fix
- Make the value a
computedinstead of writing to a signal - Do writes in event handlers or
untracked(() => ...) - Use
linkedSignalfor state derived from another signal that can also be set
Detailed fix by platform
Angular
total = computed(() => this.price() * this.qty());instead of an effect that setstotal- If unavoidable (Angular 16–18):
effect(() => {...}, { allowSignalWrites: true })
Code examples
Derive, do not write
price = signal(10);
qty = signal(2);
total = computed(() => this.price() * this.qty()); // pure
// not allowed:
// total = computed(() => { this.log.set('x'); return 1; }); // NG0600How to diagnose
- Context — computed, effect or template?
- Purpose — Can it be derived instead?
- Version — Angular version (effect rules changed in 19)?
🔧 Still not fixed?
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Last updated 15 Oct 2026