---
title: Key blocks
---

Key blocks destroy and recreate their contents when the value of an expression changes.

```html
{#key value}
	<div transition:fade>{value}</div>
{/key}
```

This is useful if you want an element to play its transition whenever a value changes instead of only when the element enters or leaves the DOM.

Wrap the `<span>` element in a key block depending on `number`. This will make the
animation play whenever you press the increment button.