Remove children of Document even if doc not in mirror (#923)

* Remove children of Document even if doc not in mirror

* fix flaky test

* Update packages/rrdom/test/diff.test.ts

Co-authored-by: Yun Feng <[email protected]>

Co-authored-by: Yun Feng <[email protected]>

packages/rrdom/src/diff.ts

@@ -316,7 +316,7 @@ function diffChildren(
          * We should delete it before insert a serialized one. Otherwise, an error 'Only one element on document allowed' will be thrown.
          */
         if (
-          replayer.mirror.getMeta(parentNode)?.type === RRNodeType.Document &&
+          parentNode.nodeName === '#document' &&
           replayer.mirror.getMeta(newNode)?.type === RRNodeType.Element &&
           (parentNode as Document).documentElement
         ) {

packages/rrdom/test/diff.test.ts

@@ -1056,6 +1056,24 @@ describe('diff algorithm for rrdom', () => {
       expect(element.tagName).toBe('DIV');
       expect(mirror.getId(element)).toEqual(2);
     });
+
+    it('should remove children from document before adding new nodes', () => {
+      document.write('<style></style>'); // old document with elements that need removing
+
+      const rrDocument = new RRDocument();
+      const docType = rrDocument.createDocumentType('html', '', '');
+      rrDocument.mirror.add(docType, getDefaultSN(docType, 1));
+      rrDocument.appendChild(docType);
+      const htmlEl = rrDocument.createElement('html');
+      rrDocument.mirror.add(htmlEl, getDefaultSN(htmlEl, 2));
+      rrDocument.appendChild(htmlEl);
+
+      diff(document, rrDocument, replayer);
+      expect(document.childNodes.length).toBe(2);
+      const element = document.childNodes[0] as HTMLElement;
+      expect(element.nodeType).toBe(element.DOCUMENT_TYPE_NODE);
+      expect(mirror.getId(element)).toEqual(1);
+    });
   });
 
   describe('create or get a Node', () => {