add reactdom

backend/resources/js/admin/index.js

@@ -1,5 +1,5 @@
 import React, { Component } from 'react';
-
+import ReactDOM from 'react-dom';
 import { BrowserRouter, Route, Switch } from 'react-router-dom';
 
 import Meeting from './meeting';

backend/resources/js/child/index.js

@@ -1,4 +1,5 @@
 import React, { Component } from 'react';
+import ReactDOM from 'react-dom';
 import Side from './side';
 
 import Meeting from './meeting';