svelte/test/runtime/samples/ignore-unchanged-attribute/main.html

<p>{{x}}</p>
<p class='{{myHelper(y)}}'></p>

<script>
	import counter from './counter.js';

	export default {
		helpers: {
			myHelper(value) {
				counter.count += 1;
				return value;
			}
		}
	};
</script>