rollup.config.js

import resolve from "@rollup/plugin-node-resolve";
import commonjs from "@rollup/plugin-commonjs";
import pkg from "./package.json";
import json from "@rollup/plugin-json";

// import { babel } from "@rollup/plugin-babel";

export default [
  // browser-friendly UMD build
  {
    input: "src/index.js",
    output: {
      dir: "dist",
      format: "esm",
    },
    plugins: [resolve(), commonjs(), json()],
  },

  // CommonJS (for Node) and ES module (for bundlers) build.
  // (We could have three entries in the configuration array
  // instead of two, but it's quicker to generate multiple
  // builds from a single configuration where possible, using
  // an array for the `output` option, where we can specify
  // `file` and `format` for each target)
  {
    input: "src/index.js",
    // external: ["d3v4"], if only we want d3 to be bundled.
    output: [
      { file: pkg.main, format: "cjs" },
      //   { file: pkg.module, format: "es" },
    ],
  },
];