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React Async provides a way for React components to subscribe for observable values.

React Async is packaged on npm:

$ npm install react-async

React Async provides a component decorator @Async which given a set of observable specifications wraps a regular React component and returns a new one which subscribes to observables and re-renders the component when new data arrives.

The basic example looks like:

import React from 'react';
import Async from 'react-async';
import Rx from 'rx';
function defineXHRObservable(url) {
  return {
    id: url,
    start() {
      return Rx.fromPromise(fetch(url))
    }
  }
}
function MyComponentObservables(props) {
  return {
    user: defineXHRObservable(`/api/user?user${props.userID}`)
  }
}
@Async(MyComponentObservables)
class MyComponent extends React.Component {
  render() {
    let {user} = this.props
    ...
  }
}

The @Async decorator injects data from observables via props so in render() method of <MyComponent /> the user property will contain the data fetched via XHR.

While React provides renderToString(element) function which can produce markup for a component, this function is synchronous. That means that it can't be used when you want to get markup from server populated with data.

React Async provides another version of renderToString(element) which is asynchronous and fetches all data defined in observable specifications before rendering a passed component tree.

First, you'd need to install fibers package from npm to use that function:

$ npm install fibers

Then use it like:

import {renderToString} from 'react-async';
renderToString(
  <Component />,
  function(err, markup) {
    // send markup to browser
  })

This way allows you to have asynchronous components arbitrary deep in the hierarchy.