svelte/test/runtime/samples/event-handler-custom/main.html

<script>
	export let x = 0;
	export let y = 0;

	function tap(node, callback) {
		function clickHandler ( event ) {
			callback({
				x: event.clientX,
				y: event.clientY
			});
		}

		node.addEventListener( 'click', clickHandler, false );

		return {
			destroy () {
				node.addEventListener( 'click', clickHandler, false );
			}
		};
	}
</script>

<button on:tap='{event => x = event.x, y = event.y}'>{x}, {y}</button>