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Using reducers to render views

December 02, 2020

Sometimes, you need to render JSX conditionally based on some conditions or state. The solution usually passes by using a ternary operator, because there are no if/else statements allowed inside JSX.

Then, our component would look like this:

const Inbox = (messages) => (
  <div>
    {message != null
      ? <Messages data={messages} />
      : <div>You don't have pending messages, yay!</div>
    }
  </div>
)

While this is great for simple components, as soon our state grows in complexity, the code can get into a mess quickly. Think of a component that fetches some data from the server. This component would have to manage the initial idle state, it should be nice to show a spinner while it's loading, then, it would show the data fetched, and of course, it should manage the errored state too. Handling this with ternary is too much.

A better way to make it work is to use a reducer to render the right view based on the request status:

const [stateApi, fetchApi] = useFetch(apiClient);

const [view, renderView] = useReducer((state, action) => {
  switch (action.status) {
    case "idle":
      return (
        <Card title="Start learning React in small pills" action={fetchApi} />
      );
    case "fetching":
      return <Loading />;
    case "fetched":
      return <Card action={fetchApi} {...stateApi.data} />;
    case "errored":
      return <div>Oops, something bad happened</div>;
    default:
      return state;
  }
}, null);

useEffect(() => {
  renderView(stateApi);
}, [stateApi.status]);

You can view a working example here. This example uses miragejs to mock the api, emotion for styling and a custom hook to handle requests.

The useFetch hook is a custom hook that tracks the state of fetch requests. It returns an object like:

{
  state: 'idle' | 'fetching' | 'fetched' | 'errored',
  data,
  error
}

It's basically a state machine of a fetch request.

As you can see, reducers are neat to handle views, making the code simple and easy to understand.

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