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<script module>
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Advanced Svelte Advanced reactivity Reactive built-ins

Svelte ships with several reactive classes that you can use in place of JavaScript built-in objects — namely Map, Set, Date, URL and URLSearchParams.

In this exercise, we could declare date using $state(new Date()) and reassign it inside the setInterval. But a nicer alternative is to use SvelteDate from svelte/reactivity:

App
<script>
	import { SvelteDate } from 'svelte/reactivity';

	let date = new SvelteDate();

	// ...
</script>
<script lang="ts">
	import { SvelteDate } from 'svelte/reactivity';

	let date = new SvelteDate();

	// ...
</script>

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<script>
	let date = new Date();
 
	const pad = (n) => n < 10 ? '0' + n : n;
 
	$effect(() => {
		const interval = setInterval(() => {
			date.setTime(Date.now());
		}, 1000);
 
		return () => {
			clearInterval(interval);
		};
	});
</script>
 
<p>The time is {date.getHours()}:{pad(date.getMinutes())}:{pad(date.getSeconds())}</p>