fix(svelte) hiding elements considers missing html elements

examples/svelte/src/routes/overview/+page.svelte

@@ -83,6 +83,12 @@
 			type: 'custom',
 			data: { label: 'Custom Node' },
 			position: { x: 150, y: 300 }
+		},
+		{
+			id: 'hideunhide',
+			data: { label: 'HIDE ME' },
+			position: { x: 300, y: 75 },
+			hidden: true
 		}
 	]);
 
@@ -179,6 +185,13 @@
 	<Panel position="top-right">
 		<button on:click={updateNode}>update node pos</button>
 		<button on:click={updateEdge}>update edge type</button>
+		<button
+			on:click={() => {
+				console.log($nodes, $nodes.length);
+				$nodes[$nodes.length - 1].hidden = !$nodes[$nodes.length - 1].hidden;
+				$nodes = $nodes;
+			}}>hide/unhide</button
+		>
 	</Panel>
 </SvelteFlow>
 

packages/svelte/src/lib/components/NodeWrapper/NodeWrapper.svelte

@@ -1,13 +1,7 @@
 <svelte:options immutable />
 
 <script lang="ts">
-  import {
-    createEventDispatcher,
-    onMount,
-    setContext,
-    SvelteComponent,
-    type ComponentType
-  } from 'svelte';
+  import { createEventDispatcher, setContext, SvelteComponent, type ComponentType } from 'svelte';
   import { get, writable } from 'svelte/store';
   import cc from 'classcat';
   import { errorMessages, Position, type NodeProps } from '@xyflow/system';
@@ -54,6 +48,8 @@
   const nodeType = type || 'default';
 
   let nodeRef: HTMLDivElement;
+  let prevNodeRef: HTMLDivElement;
+
   const nodeTypeValid = !!$nodeTypes[nodeType];
 
   if (!nodeTypeValid) {
@@ -109,13 +105,15 @@
   setContext('svelteflow__node_id', id);
   setContext('svelteflow__node_connectable', connectableStore);
 
-  onMount(() => {
-    resizeObserver?.observe(nodeRef);
-
-    return () => {
-      resizeObserver?.unobserve(nodeRef);
-    };
-  });
+  $: {
+    // hiding the noder removes html element is removed from the dom
+    if (nodeRef) {
+      resizeObserver?.observe(nodeRef);
+      prevNodeRef = nodeRef;
+    } else if (prevNodeRef) {
+      resizeObserver?.unobserve(prevNodeRef);
+    }
+  }
 
   function onSelectNodeHandler(event: MouseEvent | TouchEvent) {
     if (selectable && (!get(selectNodesOnDrag) || !draggable || get(nodeDragThreshold) > 0)) {