Transition for Sapper Navigation

_layout.svelte

<script>
	import Nav from '../components/Nav.svelte';
	import Fly from '../components/Fly.svelte';

	export let segment;
	let active = false;
	function triggerNav() {
		active = false;
		setTimeout(() => {active = true}, 1000);
	}
	setTimeout(() => {active = true}, 1000);
</script>

<style>
	main {
		position: relative;
		max-width: 56em;
		background-color: white;
		padding: 2em;
		margin: 0 auto;
		box-sizing: border-box;
	}
</style>

<Nav on:nav={triggerNav} {segment}/>

<main>
	<Fly {active}>
		<slot></slot>
	</Fly>
</main>

Fly.svelte

<script>
import { fly } from 'svelte/transition';
export let active = false;
</script>

{#if active}
    <div transition:fly={{ y: 50, duration: 300 }}>
        <slot></slot>
    </div>
{/if}

Nav.svelte

<script>
	export let segment;
	import { createEventDispatcher } from 'svelte';

	const dispatch = createEventDispatcher();

	function navigationHappened() {
		if(event.target.tagName.toLowerCase() === 'a')
		{
			dispatch('nav');
		}
	}
</script>

<style>
	nav {
		border-bottom: 1px solid rgba(255,62,0,0.1);
		font-weight: 300;
		padding: 0 1em;
	}

	ul {
		margin: 0;
		padding: 0;
	}

	/* clearfix */
	ul::after {
		content: '';
		display: block;
		clear: both;
	}

	li {
		display: block;
		float: left;
	}

	.selected {
		position: relative;
		display: inline-block;
	}

	.selected::after {
		position: absolute;
		content: '';
		width: calc(100% - 1em);
		height: 2px;
		background-color: rgb(255,62,0);
		display: block;
		bottom: -1px;
	}

	a {
		text-decoration: none;
		padding: 1em 0.5em;
		display: block;
	}
</style>

<nav on:click={navigationHappened}>
	<ul>
		<li><a class='{segment === undefined ? "selected" : ""}' href='.'>home</a></li>
		<li><a class='{segment === "about" ? "selected" : ""}' href='about'>about</a></li>

		<!-- for the blog link, we're using rel=prefetch so that Sapper prefetches
		     the blog data when we hover over the link or tap it on a touchscreen -->
		<li><a rel=prefetch class='{segment === "blog" ? "selected" : ""}' href='blog'>blog</a></li>
	</ul>
</nav>