Simply put: Components are not the right place to define these tasks. Currently working towards bringing ember-concurrency-like modifiers and derived state to redux-saga. This was a fun exercise.

☎️ React hooks for writing async tasks/workers (with cancellation and concurrency)

This library was inspired by ember-concurrency and uses posterus to run generators as cancellable async-tasks.

Redux-Saga is a fantastic tool for managing these types of tasks. I use it with redux-saga-thunk to get "derived state". It's extremely powerful. But, let's be honest - sagas are a lot of boilerplate. Sometimes, a less-powerful tool can be useful for implementing common patterns.

This library is not intended to replace redux-saga. It is component-lifecycle centric, and hopes to provide some ergonomic tools for consise async tasks:

• Derived state: Never manage boolean flags. Declaratively handle loading, error, and success states.
• Task Modes: By default, tasks can be performed multiple-times in parallel. "Modes" can be selected to modify task behavior. Using a telephone analogy:
  • Restartable: "Hang up on current caller when a new call comes in"
  • Drop: "If already on the phone, ignore incoming calls"
  • Enqueue: "Place callers on hold and handle them in order"
  • Keep Latest: ?analogy? Like drop, but the last ignored gets handled when free
• Concurrency: Easily specify concurrency limits
• Cancellation: Cancel individual task instances, or all running instances at once. Component unmounted? Everything cleans up automatically.

$ npm install --save react-use-task

import { useTask } from 'react-use-task';

const BasicTask = () => {
  const [{ isRunning, last }, perform] = useTask(function*() {
    // Hit some remote api
    yield delay(1000);
  });

  return (
    <div>
      {/* When task isRunning, button disabled & inner text changed */}
      <button disabled={isRunning} onClick={perform}>
        {isRunning ? 'Saving...' : 'Perform Task'}
      </button>

      {last && last.isSuccessful && <div>Saved!</div>}
    </div>
  );
};

const delay = (ms) => new Promise(resolve => setTimeout(resolve, ms));

import { useWorker } from "react-use-task";

const StockTicker = () => {
  const [price, setPrice] = useState();
  useWorker(function*() {
    // Infinite loop worker
    while (true) {
      yield delay(1000);
      setPrice(Math.random() * 50 + 50);
    }
  });

  if (typeof price === "undefined") {
    return <div>Loading...</div>;
  }
  return <div>Latest stock price: ${price.toFixed(2)}</div>;
};

// By mounting / unmounting the <StockTicker>, the worker loop is
//  automatically started & cancelled with the component
const App = () => {
  const [showTicker, setShow] = useState(false);
  return (
    <div>
      <button onClick={() => setShow(!showTicker)}>Toggle stock ticker</button>
      {showTicker && <StockTicker />}
    </div>
  );
};

• Non-immediate running of task (e.g. on button press)
• .drop, .restartable, .maxConcurrency task modifiers (like ember-concurrency)
• Exposing manual cancellation
• Historical state - last, lastSuccessful (like e-c)
• Code sandbox examples
• Finalize TaskInstance API - go all-in on futures?
• Improve error handling
• More docs / motivaion / examples
• Fancy visualizations (like ember-concurrency)
• Possibly split out some Posterus.Future utilities