Deferred Redux Update Pattern
Tags: react, redux
Published: 2024-07-07 07:43:12

## Introduction

When developing user interfaces with React, I often find myself juggling between different state management approaches. On one hand, Redux is great for handling large-scale application state, but on the other, useState is perfect for those small, component-specific details.

During a recent project, I was looking for a way to have the best of both worlds - using Redux for the big picture stuff while keeping the nitty-gritty details managed by useState. It wasn't straightforward, and I had to experiment quite a bit before I stumbled upon a pattern that seemed to work well.

After a few iterations and some refinement, I realized I had something that could be useful in future projects.  This pattern basically allows components to work with complex state locally, making as many changes as needed, without bombarding Redux with updates for every little change. Instead, it waits until the right moment - like when a form is submitted or a component is about to unmount - before pushing all those changes to the global Redux store.

I thought this approach might be helpful for other developers facing similar challenges, so I decided to share it here. In this article, I'll walk you through the problem this pattern solves and how it works.


## The main Use Case

The Deferred Redux Update Pattern is useful in scenarios where:

1. Your Redux store maintains complex state structures.
2. Components need to make frequent, granular updates to this state.
3. These updates don't need to be immediately reflected in the global store.

Consider a form with multiple fields, each represented in Redux. Traditional approaches might dispatch an action for every keystroke, leading to unnecessary re-renders and potential performance issues. With the Deferred Redux Update Pattern, we can buffer these changes locally and only update Redux when the form is submitted or the component unmounts.

## Rel-World Example: curldock

To better illustrate the Deferred Redux Update Pattern, let's explore how it's implemented in [curldock](https://github.com/ietxaniz/curldock), an open-source project I am working on. curldock is designed to simplify API testing, allowing developers to have an user interface for interacting with curl.

Curldock's user interface (although not finished) consists of three main components:

1. A FileExplorer component that allows interacting with a hierarchical list of curl scripts.
2. A ScriptEditor component that allows users to edit and send API requests.
3. A ResultViewer component that will allow reviewing the response from the api call.

Here's a simplified view of the application layout:


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/m9ztghawazebyazyue9r.png)

The application's data flow and state management can be visualized as follows:


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/7zraf29bpsa7vla5do50.png)

In curldock, the Deferred Redux Update Pattern is primarily used in the ScriptEditor component. Here's how it's implemented:

```typescript
import { useEffect, useRef, useState } from "react";
import { useGetCurlItemByFileId, useUpdateCurlItem } from "@/store/hooks/useCurl"
import { HttpMethod } from "@/store/slices/curlSlice";

export type Header = {
  id: string;
  name: string;
  value: string;
};

export const useScriptEditorData = (fileId: number) => {
  const [initialized, setInitialized] = useState(false);
  const getCurlItem = useGetCurlItemByFileId();
  const updateCurlItem = useUpdateCurlItem();
  const [method, setMethod] = useState<HttpMethod>(HttpMethod.GET);
  const [url, setUrl] = useState('');
  const [headers, setHeaders] = useState<Header[]>([]);
  const [bodyContent, setBodyContent] = useState('');

  const exitCallbackRef = useRef(() => {});

  exitCallbackRef.current = () => {
    if (initialized) {
      console.log(`close ${fileId} - ${url}`);
      updateCurlItem({
        fileId: fileId,
        script: {
          method: method,
          url: url,
          headers: headers.map(h => [h.name, h.value]),
          data: bodyContent,
          options: {
            verbose: true,
            insecure: false,
          }
        }
      });
    }
  };


  useEffect(() => {
    const curlItem = getCurlItem(fileId);
    if (curlItem && curlItem.script) {
      console.log(curlItem);
      const { method, url, headers, data } = curlItem.script;
      setMethod(method);
      setUrl(url);
      setHeaders(headers.map((h, index) => ({ id: index.toString(), name: h[0], value: h[1] })));
      setBodyContent(data || '');
      setInitialized(true);
    }
    console.log(`open ${fileId}`);

    return () => { exitCallbackRef.current(); }

  }, [fileId]);

  return { method, setMethod, url, setUrl, headers, setHeaders, bodyContent, setBodyContent };
}
```

This implementation allows the ScriptEditor to work with complex state locally, making as many changes as needed without immediately updating Redux. The state is only synchronized with Redux when the component unmounts or when explicitly triggered by the user (e.g., saving the script).

By using this pattern, curldock achieves several benefits:

1. Better performance and a more responsive user interface, especially when dealing with complex forms and real-time data manipulation in the ScriptEditor.
2. Cleaner code, as detailed Redux updating function calls are not needed throughout the component logic.
3. Improved state management, with clear separation between local state and global (Redux) state.


## The Problem in Detail

As I dug deeper into implementing this pattern, I ran into a few roadblocks that really made me scratch my head. The main issue I was grappling with was how to trigger the Redux update only when the component disappears, without causing unnecessary updates or running into stale data problems. At first, I thought I could manage everything with useEffect. Seems straightforward, right? But I quickly realized that if all the internal states were managed by useEffect, the cleanup function would fire every time an internal state changed. That wasn't what I wanted at all - it defeated the whole purpose of deferring updates! So, I tried using useCallback, thinking it might solve the problem. But, I ran into similar issues. It was like trying to plug a leak only to find another one popping up elsewhere. For a moment, I considered using useRef to store the state. But then I realized I'd essentially be keeping two copies of the state around. It felt like overkill, and I worried it might lead to synchronization headaches down the line. But, what if I used useRef, not for the state itself, but to manage a closing function? This approach turned out to be the key to solving my update timing problem.

But just when I thought I had it all figured out, React's Strict Mode threw me another curveball. In Strict Mode, useEffect gets called twice in each render. At first, this seemed like a minor inconvenience, but it quickly turned into a real problem. You see, the first cleanup call happens before the states are updated from Redux. If I didn't account for this, I risked storing empty data in Redux. Not exactly the behavior I was aiming for! After some more tinkering, I found a solution: a simple state that checks if all other states have been updated. It's a small addition, but it made all the difference in handling Strict Mode's double-call behavior.

These challenges really drove home the need for a more robust way to manage state updates in React-Redux applications. The solution I eventually landed on might not be perfect, but it addressed these pain points and gave me a pattern I could rely on. Let me show you how it all came together.

## The Deferred Redux Update Pattern

The Deferred Redux Update Pattern addresses these challenges by introducing a mechanism to delay Redux updates until they're necessary. Here's an overview of the key components:

1. **Local State Management**: Use React's useState for managing state within the component.

2. **Cleanup Function with useRef**: Store the cleanup function in a useRef to ensure it always has access to the most recent state.

3. **Initialization Flag**: Implement an isInitialized flag to handle React Strict Mode's double-invocation behavior.

4. **Deferred Redux Update**: Trigger the Redux update in the cleanup function, which runs when the component unmounts or when explicitly called.

Here's a code example demonstrating the pattern:

```javascript
import { useEffect, useRef, useState } from "react";
import { useDispatch } from "react-redux";

export const useDeferredReduxUpdate = (initialState, updateAction) => {
  const [state, setState] = useState(initialState);
  const [isInitialized, setIsInitialized] = useState(false);
  const dispatch = useDispatch();

  const cleanupRef = useRef(() => {});

  cleanupRef.current = () => {
    if (isInitialized) {
      dispatch(updateAction(state));
    }
  };

  useEffect(() => {
    setIsInitialized(true);
    return () => cleanupRef.current();
  }, []);

  const storeCurrentState = cleanupRef.current;

  return [state, setState, storeCurrentState];
};
```

Additionally, the hook exposes a storeCurrentState function, providing flexibility to trigger a Redux update on demand. This function can be called to push the local state to Redux at any time, such as when a user activates a "Save" button.


## Benefits and Use Cases

The Deferred Redux Update Pattern offers several key benefits:

1. **Improved Performance**: By reducing the number of Redux dispatches, we minimize unnecessary re-renders and state calculations.

2. **Cleaner Code**: The pattern encapsulates the logic for managing local state and syncing with Redux, leading to more maintainable components.

3. **Better User Experience**: With fewer global state updates, the application can feel more responsive, especially when dealing with form inputs or real-time data manipulation.

This pattern is particularly useful in scenarios such as:

- Complex forms with multiple fields
- Data visualization tools with frequent updates
- Real-time collaborative features where immediate global updates aren't necessary
- Any situation where you need to balance local interactivity with global state consistency

By implementing the Deferred Redux Update Pattern, you can significantly optimize your React-Redux applications, especially those dealing with complex state management scenarios.

## Conclusion

The Deferred Redux Update Pattern offers a powerful solution for managing complex state in React applications. By intelligently balancing local state management with global Redux updates, this pattern enhances performance, improves code clarity, and provides a smoother user experience. Whether you're working on complex forms, real-time data visualization, or collaborative features, this pattern can help enhance your state management approach. As we've seen with the curldock example, implementing this pattern can lead to more efficient and maintainable React-Redux applications. I encourage you to experiment with this pattern in your own projects and see how it can optimize your state management strategy.