[react-dom] Honor disableInputAttributeSyncing for textarea defaultValue

packages/react-dom-bindings/src/client/ReactDOMTextarea.js

@@ -11,7 +11,7 @@ import isArray from 'shared/isArray';
 
 import {getCurrentFiberOwnerNameInDevOrNull} from 'react-reconciler/src/ReactCurrentFiber';
 import {getToStringValue, toString} from './ToStringValue';
-import {disableTextareaChildren} from 'shared/ReactFeatureFlags';
+import {disableTextareaChildren, disableInputAttributeSyncing} from 'shared/ReactFeatureFlags';
 
 import {track, trackHydrated} from './inputValueTracking';
 import {queueChangeEvent} from '../events/ReactDOMEventReplaying';
@@ -75,18 +75,21 @@ export function updateTextarea(
     if (newValue !== node.value) {
       node.value = newValue;
     }
-    // TOOO: This should respect disableInputAttributeSyncing flag.
-    if (defaultValue == null) {
-      if (node.defaultValue !== newValue) {
-        node.defaultValue = newValue;
+    if (!disableInputAttributeSyncing) {
+      if (defaultValue == null) {
+        if (node.defaultValue !== newValue) {
+          node.defaultValue = newValue;
+        }
+        return;
       }
-      return;
     }
   }
   if (defaultValue != null) {
     node.defaultValue = toString(getToStringValue(defaultValue));
   } else {
-    node.defaultValue = '';
+    if (!disableInputAttributeSyncing) {
+      node.defaultValue = '';
+    }
   }
 }
 

packages/react-dom/src/__tests__/ReactDOMTextarea-test.js

@@ -436,6 +436,36 @@ describe('ReactDOMTextarea', () => {
     }
   });
 
+  it('does not update defaultValue on input event', async () => {
+    const setUntrackedValue = Object.getOwnPropertyDescriptor(
+      HTMLTextAreaElement.prototype,
+      'value',
+    ).set;
+
+    const container = document.createElement('div');
+    const root = ReactDOMClient.createRoot(container);
+    document.body.appendChild(container);
+
+    try {
+      const node = await renderTextarea(
+        <textarea value="foo" onChange={emptyFunction} />,
+        container,
+        root,
+      );
+
+      setUntrackedValue.call(node, 'bar');
+      node.dispatchEvent(
+        new Event('input', {bubbles: true, cancelable: false}),
+      );
+
+      if (ReactFeatureFlags.disableInputAttributeSyncing) {
+        expect(node.defaultValue).toBe('foo');
+      }
+    } finally {
+      document.body.removeChild(container);
+    }
+  });
+
   if (ReactFeatureFlags.disableTextareaChildren) {
     it('should ignore children content', async () => {
       const container = document.createElement('div');