rollup.config.js

import { nodeResolve } from '@rollup/plugin-node-resolve';
import commonjs from '@rollup/plugin-commonjs'
import sourceMaps from 'rollup-plugin-sourcemaps';
import typescript from 'rollup-plugin-typescript2';
import json from '@rollup/plugin-json';
import pkg from './package.json';

const libraryName = 'index';

export default {
  input: `src/${libraryName}.ts`,
  output: [
    { file: pkg.main, name: libraryName, format: 'cjs', sourcemap: true },
    { file: pkg.module, format: 'es', sourcemap: true },
  ],
  // Indicate here external modules you don't wanna include in your bundle (i.e.: 'lodash')
  external: ['cross-fetch', 'cross-fetch/polyfill', "axios"],
  watch: {
    include: 'src/**',
  },
  // https://stackoverflow.com/questions/43556940/rollup-js-and-this-keyword-is-equivalent-to-undefined
  onwarn(warning) {
    if (warning.code === 'THIS_IS_UNDEFINED') {
      return;
    }
    console.warn(warning.message);
  },
  plugins: [
    // Allow json resolution
    json(),
    // Compile TypeScript files
    typescript(),
    // Allow bundling cjs modules (unlike webpack, rollup doesn't understand cjs)
    commonjs(),
    // babel({ babelHelpers: 'bundled' }),
    // babel(),
    // Allow node_modules resolution, so you can use 'external' to control
    // which external modules to include in the bundle
    // https://github.com/rollup/rollup-plugin-node-resolve#usage
    // resolve({
    //   customResolveOptions: {
    //     moduleDirectory: 'src'
    //   },
    // }),
    nodeResolve({
      mainFields: [ "module", "browser", "main" ]
    }),


    // Resolve source maps to the original source
    // sourceMaps(),
  ],
};