old_contents: /* eslint-env node */
  
  const webpack = require('webpack');
  const packageJson = require('./package.json');
  
  const isProduction = process.env.NODE_ENV === 'production';
  
  function getLicenseComment(version) {
      return [
          'Likely $version by Ilya Birman (ilyabirman.net)',
          'Rewritten sans jQuery by Evgeny Steblinsky (volter9.github.io)',
          'Supported by Ivan Akulov (iamakulov.com), Viktor Karpov (vitkarpov.com), and contributors',
          'Inspired by Social Likes by Artem Sapegin (sapegin.me)',
      ].join('\n').replace(/\$version/g, version);
  }
  
  module.exports = {
      entry: {
          likely: './source/likely.js',
          // [] is a workaround, see https://github.com/webpack/webpack/issues/300
          'likely-commonjs': ['./source/index.js'],
      },
      output: {
          filename: '[name].js',
          library: 'likely',
          libraryTarget: 'umd',
      },
      module: {
          rules: [{
              test: /\.js$/,
              exclude: /node_modules/,
              loader: 'babel-loader',
          }],
      },
      devtool: isProduction ? 'eval' : 'source-map',
      watch: !isProduction,
      plugins: isProduction ? [
          new webpack.BannerPlugin(getLicenseComment(packageJson.version)),
      ] : [],
  };
  
new_contents: /* eslint-env node */
  
  const webpack = require('webpack');
  const packageJson = require('./package.json');
  
  const isProduction = process.env.NODE_ENV === 'production';
  
  function getLicenseComment(version) {
      return [
          'Likely $version by Ilya Birman (ilyabirman.net)',
          'Rewritten sans jQuery by Evgeny Steblinsky (volter9.github.io)',
          'Supported by Ivan Akulov (iamakulov.com), Viktor Karpov (vitkarpov.com), and contributors',
          'Inspired by Social Likes by Artem Sapegin (sapegin.me)',
      ].join('\n').replace(/\$version/g, version);
  }
  
  module.exports = {
      entry: {
          likely: './source/likely.js',
          // [] is a workaround, see https://github.com/webpack/webpack/issues/300
          'likely-commonjs': ['./source/index.js'],
      },
      output: {
          filename: '[name].js',
          library: 'likely',
          libraryTarget: 'umd',
      },
      module: {
          rules: [{
              test: /\.js$/,
              exclude: /node_modules/,
              loader: 'babel-loader',
          }],
      },
      devtool: 'source-map',
      watch: !isProduction,
      plugins: isProduction ? [
          new webpack.BannerPlugin(getLicenseComment(packageJson.version)),
      ] : [],
  };
  
subject: Use `devtool: 'source-map'` because 'eval' isn't suited for production