Sveltejs Academy · Lesson

$derived.by for Complex Derivations

Compute derived values with arbitrary logic using the callback form of $derived.

Multi-Statement Derivations

For derived values needing more than one expression, use the callback form.

let result = $derived.by(() => {
  if (count > 10) return "high";
  if (count > 5) return "medium";
  return "low";
});

The callback tracks dependencies the same way as a single-expression $derived.