---
title: "Tutorial: Setup once"
description: Tutorial — run one-time setup logic after a component first renders with the effect.once() primitive.
seo:
  title: Set up a counter with effect.once() - Ilha
---

import { example } from "./setup.examples";

Use `effect.once()` to run logic once, immediately after the component renders for the first time. Unlike `effect()`, it does not re-run on state changes — making it the right place for one-time setup such as seeding initial data or initializing third-party libraries.

The callback provides `host`, `signal`, and `hydrated` in its context, so you have direct access to the mounted element and a cancellation signal.

<Preview code={example} size="lg" />

## Similar concepts

- React: `useEffect` with an empty dependency array
- Vue: `onMounted()`
- Svelte: `onMount()`