Svelte · Senior · Question 67 of 75

Why can't a $derived expression change state?

let count = $state(0);
let doubled = $derived(count++ * 2); // ?

• ✓Correct answer: Deriveds must be pure; Svelte throws on state writes inside them, because they may run lazily and any number of times
• 2It works and increments count on each read
• 3It is allowed only in $derived.by