webpack.config.js

module.exports = ({ config }) => {
  // Transpile Gatsby module because Gatsby includes un-transpiled ES6 code.
  config.module.rules[0].exclude = [/node_modules\/(?!(gatsby)\/)/];

  // use installed babel-loader which is v8.0-beta (which is meant to work with @babel/core@7)
  config.module.rules[0].use[0].loader = require.resolve("babel-loader");

  // use @babel/preset-react for JSX and env (instead of staged presets)
  config.module.rules[0].use[0].options.presets = [
    require.resolve("@babel/preset-react"),
    require.resolve("@babel/preset-env"),
  ];

  config.module.rules[0].use[0].options.plugins = [
    // use @babel/plugin-proposal-class-properties for class arrow functions
    require.resolve("@babel/plugin-proposal-class-properties"),
    // use babel-plugin-remove-graphql-queries to remove static queries from components when rendering in storybook
    require.resolve("babel-plugin-remove-graphql-queries"),
  ];

  // Prefer Gatsby ES6 entrypoint (module) over commonjs (main) entrypoint
  config.resolve.mainFields = ["browser", "module", "main"];

  return config;
};