svelte/test/runtime/samples/transition-js-if-block-intro-outro/main.html

{#if visible}
	<div in:foo out:bar>foo then bar</div>
{/if}

<script>
	export default {
		transitions: {
			foo: function ( node, params ) {
				return {
					duration: 400,
					tick: t => {
						node.foo = t;
					}
				};
			},

			bar: function ( node, params ) {
				return {
					duration: 400,
					tick: t => {
						node.bar = t;
					}
				};
			}
		}
	};
</script>