Svelte Runes
Quick Start
Which rune? Props: $props() | Bindable: $bindable() | Computed: $derived() | Side effect: $effect() | State: $state()
Key rules: Runes are top-level only. $derived can be overridden (use const for read-only). Don't mix Svelte 4/5 syntax. Objects/arrays are deeply reactive by default.
Example
<script> let count = $state(0); // Mutable state const doubled = $derived(count * 2); // Computed (const = read-only)
$effect(() => {
console.log(`Count is ${count}`); // Side effect
});
</script>
<button onclick={() => count++}> {count} (doubled: {doubled}) </button>
Reference Files
-
reactivity-patterns.md - When to use each rune
-
migration-gotchas.md - Svelte 4→5 translation
-
component-api.md - $props, $bindable patterns
-
snippets-vs-slots.md - New snippet syntax
-
common-mistakes.md - Anti-patterns with fixes
For @attach and other template directives, see the svelte-template-directives skill.
Notes
-
Use onclick not on:click , {@render children()} in layouts
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$derived can be reassigned (5.25+) - use const for read-only
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Use createContext over setContext /getContext for type safety
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Use $inspect.trace to debug reactivity issues
-
Last verified: 2026-03-12