diff --git a/packages/react-dom/src/client/ReactDOM.js b/packages/react-dom/src/client/ReactDOM.js
index 728f775adf5..35c39fb80fd 100644
--- a/packages/react-dom/src/client/ReactDOM.js
+++ b/packages/react-dom/src/client/ReactDOM.js
@@ -550,51 +550,36 @@ function legacyRenderSubtreeIntoContainer(
   // TODO: Without `any` type, Flow says "Property cannot be accessed on any
   // member of intersection type." Whyyyyyy.
   let root: Root = (container._reactRootContainer: any);
+  let exec = function(cb){
+    cb();
+  }
+  let instance = null;
   if (!root) {
     // Initial mount
     root = container._reactRootContainer = legacyCreateRootFromDOMContainer(
       container,
       forceHydrate,
     );
-    if (typeof callback === 'function') {
-      const originalCallback = callback;
-      callback = function() {
-        const instance = getPublicRootInstance(root._internalRoot);
-        originalCallback.call(instance);
-      };
-    }
-    // Initial mount should not be batched.
-    unbatchedUpdates(() => {
-      if (parentComponent != null) {
+    exec = unbatchedUpdates;
+  } 
+  function getInstance(){
+      if (__DEV__) {
+        warnOnInvalidCallback(callback, 'render');
+      }
+      instance = getPublicRootInstance(root._internalRoot);
+      if (typeof callback === 'function') {
+         callback.call(instance);
+      }
+   }
+
+   exec(() => {
         root.legacy_renderSubtreeIntoContainer(
-          parentComponent,
+          parentComponent || null,
           children,
-          callback,
+          getInstance,
         );
-      } else {
-        root.render(children, callback);
-      }
     });
-  } else {
-    if (typeof callback === 'function') {
-      const originalCallback = callback;
-      callback = function() {
-        const instance = getPublicRootInstance(root._internalRoot);
-        originalCallback.call(instance);
-      };
-    }
-    // Update
-    if (parentComponent != null) {
-      root.legacy_renderSubtreeIntoContainer(
-        parentComponent,
-        children,
-        callback,
-      );
-    } else {
-      root.render(children, callback);
-    }
-  }
-  return getPublicRootInstance(root._internalRoot);
+    return instance;
 }
 
 function createPortal(