Fix cross-realm NodeList detection

src/morphlex.ts

@@ -264,7 +264,7 @@ class Morph {
 			this.#mapIdSets(from)
 		}
 
-		if (to instanceof NodeList) {
+		if (isNodeList(to)) {
 			this.#mapIdArraysForEach(to)
 			this.#morphOneToMany(from, to)
 		} else {
@@ -992,6 +992,10 @@ function isParentNode(node: Node): node is ParentNode {
 	return !!IS_PARENT_NODE_TYPE[node.nodeType]
 }
 
+function isNodeList(value: ChildNode | NodeListOf<ChildNode>): value is NodeListOf<ChildNode> {
+	return Object.prototype.toString.call(value) === "[object NodeList]"
+}
+
 // Find longest increasing subsequence to minimize moves during reordering
 // Returns the indices in the sequence that form the LIS
 function longestIncreasingSubsequence(sequence: Array<number | undefined>): Array<number> {

test/new/cross-realm.browser.test.ts

@@ -0,0 +1,24 @@
+import { test, expect } from "vitest"
+import { morph } from "../../src/morphlex"
+
+test("morphs to a NodeList from another realm", () => {
+	const iframe = document.createElement("iframe")
+	document.body.appendChild(iframe)
+
+	try {
+		const iframeDocument = iframe.contentDocument!
+		const template = iframeDocument.createElement("template")
+		template.innerHTML = "<span>First</span><span>Second</span>"
+
+		const parent = document.createElement("div")
+		const child = document.createElement("span")
+		child.textContent = "Original"
+		parent.appendChild(child)
+
+		morph(child, template.content.childNodes)
+
+		expect(parent.innerHTML).toBe("<span>First</span><span>Second</span>")
+	} finally {
+		iframe.remove()
+	}
+})