svelte/documentation/tutorial/05-events/01-dom-events/app-a/App.svelte

<script>
	let m = { x: 0, y: 0 };

	function handleMousemove(event) {
		m.x = event.clientX;
		m.y = event.clientY;
	}
</script>

<div>
	The mouse position is {m.x} x {m.y}
</div>

<style>
	div {
		width: 100%;
		height: 100%;
	}
</style>