svelte/test/runtime/samples/onupdate/main.html

<p ref:a>{value}</p>
<p ref:b></p>

<script>
	export default {
		onupdate({ changed, current, previous }) {
			if (changed.value) {
				this.refs.b.textContent = this.refs.a.textContent;
			}
		}
	};
</script>