How to configure Babel for production/development?

.babelrc

{
  "env": {
    "build": {
      "stage": 2
    }
  }
}

package.json

{
  ...
  "scripts": {
    "build": "webpack",
    "start": "webpack-dev-server"
  },
  ...
}

webpack.config.babel.js

...

// process.env.npm_lifecycle_event matches with "npm run"
process.env.BABEL_ENV = process.env.npm_lifecycle_event;

...