svelte/test/js/samples/event-handlers-custom/input.html

<button on:foo='foo( bar )'>foo</button>

<script>
	export default {
		methods: {
			foo ( bar ) {
				console.log( bar );
			}
		},
		events: {
			foo ( node, callback ) {
				// code goes here
			}
		}
	};
</script>