strapi/packages/strapi-helper-plugin/.babelrc

{
  "presets": [
    [
      "@babel/preset-env",
      {
        "modules": false,
        "loose": true,
        "targets": {
          "browsers": ["Since 2017"]
        }
      }
    ],
    "@babel/preset-react"
  ],
  "plugins": ["@babel/plugin-proposal-class-properties"]
}