# useUnmount

> Runs a cleanup function once, when the component unmounts.

- Category: Effects
- Package: `hookli` (install with `npm i hookli`)
- Docs: https://hookli.vercel.app/docs/use-unmount

## Signature

```ts
useUnmount(fn: () => void): void
```

## Parameters

- `fn`: `() => void` — Called exactly once when the component unmounts. The latest closure is captured in a ref, so it always sees fresh values.

## Usage

```tsx
import { useUnmount } from "hookli";

export function Demo() {
  useUnmount(() => {
    console.log("cleanup on unmount");
  });

  return <p>Watch the console when I unmount.</p>;
}
```

## Source

`src/hooks/use-unmount/use-unmount.ts`

```ts
import { useEffect, useRef } from "react";

export const useUnmount = (fn: () => void) => {
  const fnRef = useRef(fn);

  // The latest closure every render, but only invoked on unmount.
  fnRef.current = fn;

  useEffect(() => () => fnRef.current(), []);
};
```