svelte5-best-practices

Svelte 5 Best Practices

Quick Reference

Topic	When to Use	Reference
Runes	$state, $derived, $effect, $props, $bindable, $inspect	runes.md
Snippets	Replacing slots, {#snippet}, {@render}	snippets.md
Events	onclick handlers, callback props, context API	events.md
TypeScript	Props typing, generic components	typescript.md
Migration	Svelte 4 to 5, stores to runes	migration.md
SvelteKit	Load functions, form actions, SSR, page typing	sveltekit.md
Performance	Universal reactivity, avoiding over-reactivity, streaming	performance.md

Essential Patterns

Reactive State

<script>
  let count = $state(0);           // Reactive state
  let doubled =

Component Props

Snippets (replacing slots)

Event Handlers

Callback Props (replacing createEventDispatcher)

Common Mistakes

Using let without $state - Variables are not reactive without $state()
Using $effect for derived values - Use $derived instead
Using on:click syntax - Use onclick in Svelte 5
Using createEventDispatcher - Use callback props instead
Using <slot> - Use snippets with {@render}
Forgetting $bindable() - Required for bind: to work
Setting module-level state in SSR - Causes cross-request leaks
Sequential awaits in load functions - Use Promise.all for parallel requests

Svelte 5 Best Practices

Quick Reference

Topic	When to Use	Reference
Runes	$state, $derived, $effect, $props, $bindable, $inspect	runes.md
Snippets	Replacing slots, {#snippet}, {@render}	snippets.md
Events	onclick handlers, callback props, context API	events.md
TypeScript	Props typing, generic components	typescript.md
Migration	Svelte 4 to 5, stores to runes	migration.md
SvelteKit	Load functions, form actions, SSR, page typing	sveltekit.md
Performance	Universal reactivity, avoiding over-reactivity, streaming	performance.md

Essential Patterns

Reactive State

<script>
  let count = $state(0);           // Reactive state
  let doubled =

Component Props

Snippets (replacing slots)

Event Handlers

Callback Props (replacing createEventDispatcher)

Common Mistakes

Using let without $state - Variables are not reactive without $state()

Using $effect for derived values - Use $derived instead

Using on:click syntax - Use onclick in Svelte 5

Using createEventDispatcher - Use callback props instead

Using <slot> - Use snippets with {@render}

Forgetting $bindable() - Required for bind: to work

Setting module-level state in SSR - Causes cross-request leaks

Sequential awaits in load functions - Use Promise.all for parallel requests

svelte5-best-practices

Documentation

Documentation