async_iterator.jsx

import React, { Component } from 'react';
import logo from './logo.svg';
import './App.css';

const PrettyDiv = iterate(async function* (props) {
  for await (const {item} of props) {
    yield <div style={{fontSize:30}}>{item}</div>
  }
});
const Counter = iterate(async function* () {
  yield <div>Hello!</div>;
  var i = 0;
  while(true) {
    yield <PrettyDiv item={i++} />;
    await new Promise(r => setTimeout(r, 1000));
  }
}, "Counter");

const SpaceStation = iterate(async function* (props) {
  // this gets called in the constructor
  yield <div>Loading...</div>
  try {
    let position = await fetch('http://api.open-notify.org/iss-now.json').then(x => x.json());
    let { latitude, longitude } = position.iss_position;
    yield <div> The ISS is at {latitude} x {longitude} </div>
  } catch (e) {
    // error handling
    yield <div> Error Loading Space Station Location </div>
  } finally {
    // this gets called on unmount
  }
}, "SpaceStation");

function pushedIterator(props) {
  const pressure = [props];
  const backPressure = [];
  let done = false;
  return {
    next(/* ignored */) {
      return new Promise(r => {
        if (pressure.length) {
          r({value: pressure.shift(), done: false});
        } else {
          if (done) {
            r({value: undefined, done: true});
          }
          backPressure.push(r);
        }
      });
    },
    return() {
      done = true;
    },
    throw() {},
    push(value) {
      if(pressure.length || !backPressure.length) {
        pressure.push(value);
      } else {
        const resolve = backPressure.shift(); 
        resolve({value, done: false });
      }
    },
    [Symbol.asyncIterator]() {
      return this;
    }
  }
}
function iterate(iterator, name) {
  return class Hooked extends Component {
    constructor(props) {
      super(props);
      this.name = name;
      this.value = null;
      this.propsIterator = pushedIterator(props);
      this.iterator = iterator(this.propsIterator);
    }
    async componentDidMount() {
      for await (const item of this.iterator) {
        this.value = item;
        if(this.value === undefined) debugger;
        await new Promise(r => this.forceUpdate(r));
      }
    }
    componentWillUnmount() {
      iterator.close();
    }
    shouldComponentUpdate(nextProps) {
      this.propsIterator.push(nextProps);
      return false;
    }
    render() {
      return this.value;
    }
  }
}
class App extends Component {
  render() {
    return (
      <div className="App">
        <header className="App-header">
          <img src={logo} className="App-logo" alt="logo" />
          <Counter />
          {/* <SpaceStation></SpaceStation> */}
        </header>
      </div>
    );
  }
}

export default App;