rollup.config.js

import ts from '@rollup/plugin-typescript';
import { promises as fs } from 'fs';

const isCJSBuild = process.env.MODE === 'cjs';

const commonjsPkgJSONPlugin = () => {
  return {
    name: 'commonjsPkgJSONPlugin',
    writeBundle: async () => {
      if (isCJSBuild === true) {
        await fs.writeFile(
          'dist/cjs/package.json',
          JSON.stringify({
            type: 'commonjs',
          })
        );
      } else {
        await fs.copyFile('package.json', 'dist/package.json');
        await fs.copyFile('README.md', 'dist/README.md');
      }
    },
  };
};

export default {
  input: ['src/index.ts', 'src/relay.ts'],
  output: [
    {
      dir: isCJSBuild ? 'dist/cjs' : 'dist',
      format: isCJSBuild ? 'cjs' : 'esm',
      entryFileNames: isCJSBuild ? '[name].cjs' : '[name].js',
    },
  ],
  plugins: [
    ts({ tsconfig: isCJSBuild ? 'tsconfig.cjs.json' : 'tsconfig.json' }),
    commonjsPkgJSONPlugin(),
  ],
  external: ['graphql'],
};