In today’s connected world, it’s essential for applications to handle offline states gracefully. When working with state management libraries like Immer, there are several strategies you can employ to handle offline state effectively. In this article, we’ll explore a few approaches that can help you maintain a seamless user experience even when the connection is lost.

1. Leveraging Local Storage

One of the simplest ways to handle offline state is by leveraging the browser’s local storage. With Immer, you can easily persist your state to local storage and retrieve it when the application comes back online. This approach ensures that users can continue working and seamlessly transition between online and offline states without losing any data.

Here’s an example of how you can use Immer’s produceWithPatches function to handle offline state with local storage:

import produceWithPatches from "immer";
import { useState, useEffect } from "react";

// Initialize state from local storage
const initialState = JSON.parse(localStorage.getItem("appState")) || {
  // Default state
};

const App = () => {
  const [state, setState] = useState(initialState);

  useEffect(() => {
    // Save state to local storage on every state change
    localStorage.setItem("appState", JSON.stringify(state));
  }, [state]);

  const updateState = (draft) => {
    const [newState, patches] = produceWithPatches(state, draft);
    setState(newState);

    // Handle applying the patches when online
    if (navigator.onLine) {
      // Send patches to the server and update the remote state
    }
  };

  // Rest of the component code
};

In this example, we initialize the state with the data stored in local storage. We then use the produceWithPatches function provided by Immer to update the state. On every state change, we save the updated state to local storage. When the application is back online, we can send the patches to the server and update the remote state accordingly.

2. Optimistic Updates

Another effective strategy for handling offline state is through optimistic updates. With optimistic updates, you update the UI with the assumption that the remote server will accept the changes, and then later sync the local and remote states when the connection is restored.

Here’s an example of using optimistic updates with Immer:

import produce from "immer";

const App = () => {
  const [state, setState] = useState(/* initial state */);
  const [pendingUpdates, setPendingUpdates] = useState([]);

  const updateState = (draft) => {
    setPendingUpdates((updates) => [...updates, draft]);

    // Update UI with optimistic changes
    setState(produce(state, draft));
  };

  const syncOfflineUpdates = async () => {
    // Send pending updates to the server and update the remote state
    for (const draft of pendingUpdates) {
      await serverApi.updateState(draft);

      // Remove the applied update from the pending list
      setPendingUpdates((updates) => updates.slice(1));
    }
  };

  useEffect(() => {
    // Sync offline updates when back online
    if (navigator.onLine) {
      syncOfflineUpdates();
    }
  }, []);

  // Rest of the component code
};

In this example, we maintain a separate list of pending updates. Whenever a state update is triggered while offline, we add the update to the pending list and apply the optimistic change to the UI. When the connection is restored, we iterate through the pending updates, sending them to the server and updating the remote state. This way, the UI stays responsive during offline periods, and any changes made are queued for later synchronization with the server.

#WrapUp #OfflineStateHandling