export the right thing

rollup-react-helper.js

const fetch = require('node-fetch')

const importMap = {
    react: "react/umd/react.production.min.js",
    'react-dom': "react-dom/umd/react-dom.production.min.js",
}

const imported = {}

function nullish(a, b) {
    return a == null ? b : a // nodejs 14 can do a ?? b
}

function fakeRequire(path) {
    return nullish(imported[path], {})
}

async function listExports(lib, deps = {}) {
    const path = nullish(importMap[lib], lib)
    const url = 'https://cdn.jsdelivr.net/npm/' + path
    const raw = await fetch(url).then(r => r.text())
    const code = 'var exports={},module={exports};' + raw + 'return exports'
    const result = imported[lib] = Function('require', code)(fakeRequire)
    return Object.keys(result).filter(e => !e.startsWith('_'))
}

;(async function() {
    const memo = {}
    const work = async a => memo[a] = await listExports(a)
    await work('react')
    await work('react-dom')
    function helper(a, b) {
        const snippet = '{ ' + memo[a].join(', ') + ' }'
        console.log('const ' + snippet + ' = ' + b + ';')
        console.log('export ' + snippet + ';')
        console.log('export default ' + b + ';')
    }
    helper('react', 'React')
    // helper('react-dom', 'ReactDOM')
})()
// outputs: (react 17.0.1)
/*
const { Fragment, StrictMode, Profiler, Suspense, Children, Component, PureComponent, cloneElement, createContext, createElement, createFactory, createRef, forwardRef, isValidElement, lazy, memo, useCallback, useContext, useDebugValue, useEffect, useImperativeHandle, useLayoutEffect, useMemo, useReducer, useRef, useState, version } = React;
export { Fragment, StrictMode, Profiler, Suspense, Children, Component, PureComponent, cloneElement, createContext, createElement, createFactory, createRef, forwardRef, isValidElement, lazy, memo, useCallback, useContext, useDebugValue, useEffect, useImperativeHandle, useLayoutEffect, useMemo, useReducer, useRef, useState, version };
export default React;
*/