webpack.config.rules.js

const rules = [
  {
    test: /\.js?$/,
    enforce: "pre",
    loader: "prettier-loader",
    options: {
      parser: "babel",
      singleQuote: true,
      semi: false,
      jsxBracketSameLine: true,
      tabWidth: 2
    }
  },
  {
    test: /\.js$/,
    exclude: /node_modules/,
    use: {
      loader: "babel-loader"
    }
  }
]

module.exports = rules