svelte/documentation/tutorial/10-transitions/09-key-blocks/text.md

title
Key blocks

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

{#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.