react-grid-layout/.babelrc.js

// @flow

const es6Compat =
  process.env.BABEL_ES_COMPAT === "6" || process.env.NODE_ENV === "test";

module.exports = {
  presets: [
    [
      "@babel/preset-env",
      {
        targets: es6Compat ? "maintained node versions" : "> 0.25%, not dead"
      }
    ],
    "@babel/react",
    "@babel/preset-flow"
  ],
  plugins: [
    "@babel/plugin-transform-flow-comments",
    "@babel/plugin-transform-class-properties",
    "babel-plugin-preval"
  ]
};