I've just faced to unpredictable situation during using custom webpack config. I will try to explain the problem.

This is my simple app (file index.js):

console.log('!!this', this);

This is my webpack config (file webpack.config.js):

const path = require('path');
const HtmlWebpackPlugin = require('html-webpack-plugin');

module.exports = {
  mode: 'development',
  entry: './src/index.js',
  plugins: [
    new HtmlWebpackPlugin({
      template: './public/index.html',
    }),
  ],
  output: {
    path: path.resolve(__dirname, 'dist'),
    filename: 'bundle.js',
  },
  resolve: {
    extensions: ['.js', '.jsx', '.json'],
  },
  module: {
    rules: [
      {
        test: /\.jsx?$/,
        loader: 'babel-loader',
      },
      {
        test: /\.css$/i,
        use: ['style-loader', 'css-loader'],
      },
      {
        test: /\.scss$/,
        use: [
          'style-loader',
          'css-loader',
          {
            loader: 'sass-loader',
            options: {
              additionalData: `@import './src/constants/global';`,
            },
          },
        ],
      },
      {
        test: /\.(png|svg|jpe?g|gif)$/i,
        use: [
          {
            loader: 'file-loader',
            options: { name: 'img/[name].[ext]' },
          },
          'image-webpack-loader',
        ],
      },
    ],
  },
};

This is my npm script for launching the app (file package.json):

"scripts": {
    "dev": "webpack serve --config webpack.config.js",
},

As a result I see the next picture - all code executes twice (index.js, VM787 index.js). In addition to that, if I use data fetching callback in my app with this configuration, I will see two equal requests in the Network tab.

Who knows what is the reason for that and how to resolve it?

Thanks!