.babelrc

{
  "env": {
    "testing": {
      "presets": [
        ["@babel/preset-env", {
          "targets": {
            "node": "current"
          }
        }],
        "power-assert"
      ]
    }
  },
  "presets": [["@babel/preset-env", {
    "targets": {
      "browsers": [
        "last 2 chrome versions",
        "last 2 firefox versions",
      ],
      "node": "6.10"
    }
  }]],
  "plugins": [
    "@babel/plugin-proposal-object-rest-spread",
    "@babel/plugin-proposal-class-properties"
  ]
}