Используем разные конфиги Babel для серверного и клиентского кода

.babelrc

{
  "env": {
    "node4": {
      "presets": ["es2015-node4"]
    },
    "node5": {
      "presets": ["es2015-node5"]
    },
    "development": {
      "presets": ["es2015"]
    }
  }
}

package-with-scripts.json

{
  "name": "babel-es2015-config",
  "scripts": {
    "build-client": "babel client.js --out-file client-compiled.js",
    "server-node4": "BABEL_ENV=node4 babel-node server.js",
    "server-node5": "BABEL_ENV=node5 babel-node server.js"
  },
  "devDependencies": {
    "babel-cli": "^6.6.5",
    "babel-preset-es2015": "^6.6.0",
    "babel-preset-es2015-node4": "^2.0.3",
    "babel-preset-es2015-node5": "^1.2.0"
  }
}

package.json

{
  "name": "babel-es2015-config",
  "devDependencies": {
    "babel-cli": "^6.6.5",
    "babel-preset-es2015": "^6.6.0",
    "babel-preset-es2015-node4": "^2.0.3",
    "babel-preset-es2015-node5": "^1.2.0"
  }
}