webpack.config.js

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

const HtmlWebpackPluginConfig = new HtmlWebpackPlugin({
  template: `${__dirname}/app/index.html`,
  filename: 'index.html',
  inject: 'body',
});

const webpack = require('webpack');

const noEnvVar = (name) => {
  throw new Error(`${name} environment variable is undefined. Please provide it to fix this error.`);
};

const DefinePluginConfig = new webpack.DefinePlugin({
  COGNITO_POOL_ID: JSON.stringify(process.env.COGNITO_POOL_ID || noEnvVar('COGNITO_POOL_ID')),
  COGNITO_APP_CLIENT_ID: JSON.stringify(process.env.COGNITO_APP_CLIENT_ID || noEnvVar('COGNITO_APP_CLIENT_ID')),
});

const BabelLoader = {
  test: /\.(js|jsx)$/,
  exclude: /node_modules/,
  loader: 'babel-loader',
};

const CSSLoader = {
  test: /\.css$/,
  loader: 'style-loader!css-loader?modules!postcss-loader',
};

const JSONLoader = {
  test: /\.json$/,
  loader: 'json-loader',
};

module.exports = {
  entry: [
    './app/index.js',
  ],
  output: {
    path: `${__dirname}/dist`,
    filename: 'index_bundle.js',
  },
  resolve: {
    extensions: ['.js', '.jsx'],
  },
  module: {
    loaders: [BabelLoader, CSSLoader, JSONLoader],
  },
  plugins: [HtmlWebpackPluginConfig, DefinePluginConfig],
};