React 19 HMR Issues: Preventing Full Page Reloads and Pre-Reload Errors in a Hello-World Project

Below are a few suggestions to address both issues:

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1. Use React Refresh for Fast, Non‐Destructive Updates

Currently you’re handling HMR “manually” by accepting the module in index.js. While that works to some degree, React 19 works best with HMR when using the official React Refresh integration. Without it, changes may lead to full page reloads and even brief errors when React sees mismatches.

To fix this, install and configure both the Babel plugin and the Webpack plugin for React Refresh:

1. Install Required Packages

   BASHCopied
   npm install --save-dev @pmmmwh/react-refresh-webpack-plugin react-refresh

2. Update Babel Configuration

   (If you have a .babelrc or babel.config.json, add the react-refresh plugin to your development configuration.)

   Example (.babelrc):

   JSONCopied
   {
     "presets": [
       "@babel/preset-env",
       "@babel/preset-react"
     ],
     "plugins": [
       "react-refresh/babel"
     ]
   }

3. Update webpack.config.js

   Import and add the plugin only in development mode:

   JAVASCRIPTCopied
   const path = require('path');
   const HtmlWebpackPlugin = require('html-webpack-plugin');
   const ReactRefreshWebpackPlugin = require('@pmmmwh/react-refresh-webpack-plugin');
   
   const isDevelopment = process.env.NODE_ENV !== 'production';
   
   module.exports = {
       mode: isDevelopment ? 'development' : 'production',
       entry: './src/index.js',
       output: {
           path: path.resolve(__dirname, 'dist'),
           filename: 'bundle.[contenthash].js',
           clean: true
       },
       devServer: {
           static: {
               directory: './dist',
               publicPath: '/apps/chat-contests/dev'
           },
           port: 1010,
           hot: true,
           allowedHosts: 'all',
           client: {
               webSocketURL: {
                   protocol: 'wss',
                   port: 443,
                   hostname: 'my-hostname.com',
                   pathname: '/chat-contests-ws'
               }
           }
       },
       module: {
           rules: [
               {
                   test: /\.jsx?$/,
                   exclude: /node_modules/,
                   use: {
                       loader: 'babel-loader',
                       options: {
                           // Make sure Babel only uses react-refresh in development:
                           plugins: [
                               isDevelopment && require.resolve('react-refresh/babel')
                           ].filter(Boolean)
                       }
                   }
               },
               {
                   test: /\.css$/,
                   use: [ 'style-loader', 'css-loader' ]
               }
           ]
       },
       resolve: {
           extensions: ['.js', '.jsx']
       },
       plugins: [
           new HtmlWebpackPlugin({
               template: './public/index.html'
           }),
           isDevelopment && new ReactRefreshWebpackPlugin()
       ].filter(Boolean)
   };

By using React Refresh these changes should update only the modified component (like your App) without a full page reload—and without showing the transient errors caused by a complete remount.

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2. Avoid Hydration or Refresh Errors

Your error message (shown immediately before the full page reload) may be caused by React’s detection of mismatches between the previously mounted components and the updated ones. When using React Refresh with proper boundaries, React keeps the component’s state and avoids remounting the tree. This minimizes display of such errors.

Make sure that:

• The render function (and React’s root API) is used only once.
• The component’s tree remains consistent between refreshes.
• No extraneous side effects occur on hot updates.

Using the React Refresh setup described above is the recommended way to get “true” HMR working (updating App without a full page reload) in React 19.

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3. Cleaning Up Your Hot Module Code

Once you enable React Refresh via the Babel and Webpack plugins, you no longer need to handle module replacement manually. In your src/index.js you can simply do:

JAVASCRIPTCopied
import React from 'react';
import { createRoot } from 'react-dom/client';
import App from './App';

const app = createRoot(document.getElementById('app'));
app.render(<App />);

if (module.hot) {
  module.hot.accept();
}

Even though the module.hot.accept() call is optional with React Refresh, leaving it in place won’t hurt—but using the refresh plugin will ensure that component updates are non-destructive and smooth.

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Summary

• Issue 1 (Error before reload): Likely due to a full remount caused by an incomplete HMR setup. Integrating React Refresh minimizes these remounts and prevents transient errors.

• Issue 2 (Page reload instead of updating App): Proper configuration via the React Refresh Babel and Webpack plugins enables HMR to update just the changed module (App) without a full page reload.

Following these steps should resolve both issues and give you a fast, error-free hot-reloading development experience with React 19.