effect in Svelte
From the Svelte cheat sheet · Runes (Svelte 5) · verified Jul 2026
$effect
Side effects and lifecycle
javascript
<script>
import { untrack } from 'svelte';
let count = $state(0);
// Simple effect
$effect(() => {
console.log('Count:', count);
});
// Effect with cleanup
$effect(() => {
const timer = setInterval(() => {
console.log('Tick');
}, 1000);
return () => clearInterval(timer);
});
</script>🔄 Replaces onMount, afterUpdate, and onDestroy
🧹 Return cleanup function for teardown logic
📍 $effect.pre runs before DOM updates
🎯 untrack() prevents dependency tracking
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