了解过渡的开始和结束可能会很有用。Svelte调度监听事件，像监听其他任何DOM事件一样：

<p
	transition:fly="{{ y: 200, duration: 2000 }}"
	on:introstart="{() => status = 'intro started'}"
	on:outrostart="{() => status = 'outro started'}"
	on:introend="{() => status = 'intro ended'}"
	on:outroend="{() => status = 'outro ended'}"
>
	Flies in and out
</p>

示例代码

• App.svelte

<script>
	import { fly } from 'svelte/transition';

	let visible = true;
	let status = 'waiting...';
</script>

<p>status: {status}</p>

<label>
	<input type="checkbox" bind:checked={visible}>
	visible
</label>

{#if visible}
	<p
		transition:fly="{{ y: 200, duration: 2000 }}"
		on:introstart="{() => status = 'intro started'}"
		on:outrostart="{() => status = 'outro started'}"
		on:introend="{() => status = 'intro ended'}"
		on:outroend="{() => status = 'outro ended'}"
	>
		Flies in and out
	</p>
{/if}