fix: Document.cloneNode(true) produces null .body & .head (closes #157)

src/dom/document.ts

@@ -282,6 +282,31 @@ export class Document extends Node {
     return node;
   }
 
+  // FIXME: This is a bad solution. The correct solution
+  // would be to make `.body` and `.head` dynamic getters,
+  // but that would be a breaking change since `.body`
+  // and `.head` would need to be typed as `Element | null`.
+  // Currently they're typed as `Element` which is incorrect...
+  cloneNode(deep?: boolean): Document {
+    const doc = super.cloneNode(deep) as Document;
+
+    for (const child of doc.documentElement?.childNodes || []) {
+      switch (child.nodeName) {
+        case "BODY": {
+          doc.body = child as Element;
+          break;
+        }
+
+        case "HEAD": {
+          doc.head = child as Element;
+          break;
+        }
+      }
+    }
+
+    return doc;
+  }
+
   querySelector(selectors: string): Element | null {
     return this._nwapi.first(selectors, this);
   }

test/units/Document-cloneNode.ts

@@ -0,0 +1,19 @@
+import { DOMParser, Document } from "../../deno-dom-wasm.ts";
+import { assertStrictEquals as assertEquals } from "https://deno.land/std@0.85.0/testing/asserts.ts";
+
+Deno.test("Document.cloneNode has non-null .body & .head when they exist", () => {
+  const doc = new DOMParser().parseFromString(
+    `<div></div>`,
+    "text/html",
+  )!;
+  const docClone = doc.cloneNode(true);
+
+  assertEquals(docClone.body?.localName, "body");
+  assertEquals(docClone.head?.localName, "head");
+
+  const emptyDoc = new Document();
+  const emptyDocClone = emptyDoc.cloneNode(true);
+
+  assertEquals(emptyDocClone.body, null);
+  assertEquals(emptyDocClone.head, null);
+});