execute error page hooks

test/apps/errors/src/routes/_error.svelte

@@ -1,3 +1,17 @@
+<script>
+	import { onMount, onDestroy } from 'svelte'
+
+	export let status, error = {};
+
+	let mounted = false;
+
+	onMount(() => {
+		mounted = 'success';
+	})
+</script>
+
 <h1>{status}</h1>
 
-<p>{error.message}</p>
+<h2>{mounted}</h2>
+
+<p>{error.message}</p>