solana-program-library/token/js/babel.rollup.config.json

{
  "presets": [
    [
      "@babel/preset-env",
      {
        "modules": false,
        "targets": {
          "node": "10"
        }
      }
    ],
    "@babel/preset-flow"
  ],
  "plugins": [
    "@babel/plugin-transform-runtime",
    "@babel/plugin-proposal-class-properties"
  ]
}