title: Webpack production mode - NODE_ENV undefined
body: <p>I want to make production build of my app using webpack:</p>
  
  <pre><code>"scripts": {
      "build": "webpack --mode production",
    },
  </code></pre>
  
  <p>In my webpack.config.js I have this line what I am using in whole config:</p>
  
  <pre><code>const isDevelopment = process.env.NODE_ENV !== 'production';
  
  Usage example:
  {
    test: /\.s(a|c)ss$/,
      exclude: /\.module.(s(a|c)ss)$/,
      loader: [
        isDevelopment ? 'style-loader' : MiniCssExtractPlugin.loader,
                      'css-loader',
                      {
                          loader: 'sass-loader',
                          options: {
                              sourceMap: isDevelopment
        }
      }
    ]
  }
  </code></pre>
  
  <p>but <code>process.env.NODE_ENV</code> is always <code>undefined</code>.</p>
  
  <p>I am on Windows 10</p>
  
  <p>Am I doing something wrong?</p>