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

<button on:tap='set({ z: event.answer })'>{{z}}</button>

<script>
	export default {
		data: () => ({
			z: '???',
			answer: '42'
		}),

		events: {
			tap ( node, callback ) {
				const clickHandler = event => {
					callback({
						answer: this.get( 'answer' )
					});
				};

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

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