fix for ssr + dynamic imports with webpack

ensure.js

function ensure(moduleId, fn, done){
  if(__webpack_modules__[moduleId]) {       //eslint-disable-line no-undef
    return done(undefined, __webpack_require__(moduleId))        //eslint-disable-line no-undef
  } 
  fn().then(Module => done(undefined, Module), done)
}


// usage
ensure(require.resolveWeak('./x.js'), 
  async () => import('./x.js'),   
  // or use require.ensure for predictable chunk names 
  // () => require.ensure([], require => require('./x.js'), chunk)
  (err, Module) => {
    // this could be possibly sync 
    // if you've loaded your chunks in the correct order 
    // so rehydrating with react will be fine 
    // ... do as you will!
  })