What's wrong with setting up Webpack?

Question

webpack

The bottom line is this: I'm setting up the webpack builder, I want to compile all the less files and add them all into one css. Got an error...

Code:

const path = require('path');
const webpack = require('webpack');

// Plugins

const ExtractTextPlugin = require('extract-text-webpack-plugin');

// Module settings
module.exports = {
  // Путь к проекту
  context: path.resolve(__dirname, 'src'),

  // Точки входа JS
  entry: {
    // Основной файл приложения
    app: [
      './js/app.js',
      './less/main.less'
    ],
  },
            
  // Путь для собранных файлов

  output: {
    filename: 'js/[name].js',
    path: path.resolve(__dirname, 'dist'),
    publicPath: '../'
  },

  // devServer configuration

  devServer: {
    contentBase: './app'
  },

  module: {
    rules: [
      // less
      {
        test: /\.less$/,
        use: ExtractTextPlugin.extract({
          use: [
            {
              loader: 'css-loader',
              option: { sourceMap: true }
            },
            {
              loader: 'less-loader',
              option: { sourceMap: true }
            },
          ],
          fallback: 'style-loader',
        })
      },
    ],
  },

  plugins: [
    new ExtractTextPlugin(
      './css/[name].css'
    ),
  ],
}

Answer 1

option s : { sourceMap: true }