fix: prevent ProseMirror document mutation during server-side rendering (#7296)

Author: bdbch

.changeset/add-ssr-guard-table-of-contents--steady-sparrow.md

@@ -0,0 +1,5 @@
+---
+"@tiptap/extension-table-of-contents": patch
+---
+
+Fixed a bug that mutated the ProseMirror document during server-side rendering, which could cause "Invalid content for node doc" errors.

packages/extension-table-of-contents/src/plugin.ts

@@ -13,6 +13,11 @@ export const TableOfContentsPlugin = ({
     key: new PluginKey('tableOfContent'),
 
     appendTransaction(transactions, _oldState, newState) {
+      // Avoid running on the server where `window` / DOM is not available.
+      if (typeof window === 'undefined') {
+        return null
+      }
+
       const tr = newState.tr
       let modified = false
 

packages/extension-table-of-contents/src/tableOfContents.ts

@@ -262,6 +262,11 @@ export const TableOfContents = Extension.create<TableOfContentsOptions, TableOfC
   },
 
   onCreate() {
+    // Avoid mutating the document during server-side rendering.
+    if (typeof window === 'undefined' || !this.editor.view) {
+      return
+    }
+
     const { tr } = this.editor.state
     const existingIds: string[] = []