Svelte components, slots, and error handling.
4 articles
Update nested data in Svelte the right way. With a writable store, use update() and return a new object (immutability keeps reactivity). In Svelte 5, $state is deeply reactive — mutate nested properties directly.
<svelte:fragment> is not a general performance trick — Svelte already allows multiple root elements. It exists to pass several elements into a NAMED slot without an extra wrapper node. In Svelte 5, snippets supersede it.
Svelte error handling: the await catch branch, <svelte:boundary> in Svelte 5, and +error.svelte in SvelteKit. There is no <svelte:error> element.
Svelte slot content is resolved by the parent at compile time — you can't swap it imperatively after a component is created. Drive it with a prop or {#if}, or use Svelte 5 snippets passed as props for a truly reassignable slot.