[Section] Modelling async data with ADT

[piotrwitek]

Add a new section with patterns on how to model data structures using static-typing to make the incorrect state unrepresentable. This should prevent a lot of edge cases and various display bugs by constraining our data structure to only represent correct state and also require our UI components to always handle all possible representable states when implementing a view components for the particular piece of data.

Rough sketch for this pattern:

Instead of modelling your remote data in reducer like this:

type State = {
  readonly isFetching: boolean,
  readonly error: string | null,
  readonly users: Array<User>,
};

Do it like this:

// we will use a generic union type, that can be designed specifically for our application needs
// it will set common conventions in reducers but also the way of handling different states of the components
// when fetching remote data
type RemoteData<E, D> =
  | { status: 'INITIAL' }
  | { status: 'LOADING' }
  | { status: 'ERROR', error: E }
  | { status: 'SUCCESS', data: D };

// declare your state as simple as that
type State = RemoteData<Error, Array<User>>

Now implement your component like this:

type Props = {
  usersModel: RemoteData<Error, Array<User>>,
};

const ViewComponent: React.SFC<Props> = ({ usersModel }) => {
  if (usersModel.status === 'INITIAL') {
    return null;
  } else if (usersModel.status === 'LOADING') {
    return <div>Loading...</div>;
  } else if (usersModel.status === 'ERROR') {
    return <div>An error has occurred { usersModel.error }</div>;
  }

  return (
    <>
      { usersModel.data.map(user => { ... }) }
    </>
  );
}

connect((state: State) => {
  usersModel: usersModelSelector(state),
})(ViewComponent);

[IssueHuntBot]

@boostio funded this issue with $40. Visit this issue on Issuehunt

[IssueHuntBot]

@issuehunt has funded $50.00 to this issue.

---

• Submit pull request via IssueHunt to receive this reward.
• Want to contribute? Chip in to this issue via IssueHunt.
• Checkout the IssueHunt Issue Explorer to see more funded issues.
• Need help from developers? Add your repository on IssueHunt to raise funds.

[nikican]

Hi @piotrwitek , I've found 2 libraries that solve this: https://github.com/devexperts/remote-data-ts https://github.com/abraham/remotedata

Hope it helps.