babel.config.js

module.exports = function(api) {
  var validEnv = ["development", "test", "production"];
  var currentEnv = api.env();
  var isDevelopmentEnv = api.env("development");
  var isProductionEnv = api.env("production");
  var isTestEnv = api.env("test");

  if (!validEnv.includes(currentEnv)) {
    throw new Error(
      "Please specify a valid `NODE_ENV` or " +
        '`BABEL_ENV` environment variables. Valid values are "development", ' +
        '"test", and "production". Instead, received: ' +
        JSON.stringify(currentEnv) +
        "."
    );
  }

  return {
    presets: [],
    plugins: [
      "babel-plugin-macros",
      "@babel/plugin-syntax-dynamic-import",
      isTestEnv && "babel-plugin-dynamic-import-node",
      [
        "@babel/plugin-proposal-class-properties",
        {
          loose: true
        }
      ]
    ].filter(Boolean)
  };
};