React Query focusManager and onlineManager

Anton Ioffe - March 5th 2024 - 10 minutes read

In the constantly evolving landscape of modern web development, creating responsive and efficient React applications demands not only keen coding skills but also an astute understanding of user and network interactions. Enter React Query's focusManager and onlineManager - two pivotal tools designed to elevate the user experience by seamlessly managing data freshness and application responsiveness in relation to user focus and network changes. This article dives deep into the intricacies of integrating and leveraging these features in your React applications. Through practical code examples, real-world scenarios, and an exploration of common pitfalls and best practices, we'll guide you on a journey to harness the full potential of focusManager and onlineManager, ensuring your projects stand out in terms of performance and user satisfaction. Whether you're looking to optimize your current projects or future-proof your applications, the insights provided here will open new horizons in your development endeavors.

Understanding React Query's focusManager and onlineManager

In modern web and mobile application development, managing the state of data fetching based on user focus and network status changes plays a crucial role in enhancing the user experience. React Query's focusManager and onlineManager are sophisticated tools designed for this purpose. The focusManager is responsible for handling focus-related events in applications. This means that it listens for when the application or a specific part of it comes into or goes out of focus. When the application comes into focus, React Query can automatically trigger data fetching operations to refresh the application's state with the latest data. This ensures that users always interact with the most current information without having to manually refresh the application.

On the other hand, the onlineManager is tasked with monitoring the network state of the application. It listens for changes in the network connectivity status, such as when the application goes offline or comes back online. In scenarios where an application transitions from an offline to an online state, the onlineManager can instruct React Query to refetch data that might have failed or been skipped during the offline period. This guarantees that once a user's device regains internet connectivity, the application quickly updates its data, thereby enhancing the user’s experience by keeping the application's state synchronized with the server.

Both focusManager and onlineManager function by subscribing to specific events related to focus and network connectivity, respectively. For instance, focusManager may listen to window focus events in web applications, while onlineManager relies on network information APIs or libraries to detect connectivity changes. These mechanisms enable React Query to provide developers with auto-managed queries and mutations that reflect the latest state based on user interaction and network status, seamlessly bridging the gap between the user's experience and the application's data management strategies.

The integration of focusManager and onlineManager into React Query undeniably streamlines the process of ensuring data freshness and responsiveness. By automatically handling data refetching in response to these critical events, applications become more intelligent and user-friendly. Users no longer need to worry about outdated information or manual refreshes upon regaining focus or connectivity, as React Query handles these scenarios in the background, offering a smooth and intuitive experience.

Moreover, the effectiveness of focusManager and onlineManager extends beyond just user convenience; it also contributes to optimizing application performance. By smartly managing when to fetch or refetch data, these tools help in reducing unnecessary network requests and prioritize fetching fresh data only when it makes sense - i.e., when the user is actively interacting with the application, or when the device reconnects to the internet. This not only conserves bandwidth but also ensures that the application remains responsive and efficient, further enhancing the overall user experience.

Integrating focusManager in Your React Query Setup

Integrating focusManager into your React Query setup involves a few thoughtful considerations aimed at enhancing application performance while ensuring a smooth user experience. One significant advantage of using focusManager is its capacity to control the behavior of data fetching when an app comes into focus. This can be particularly beneficial in single-page applications (SPAs) where minimizing network requests while keeping data fresh is crucial.

import { focusManager } from 'react-query';

const handleFocus = () => {

if (typeof window !== 'undefined' && window.addEventListener) {
    window.addEventListener('focus', handleFocus);

    // Remember to clean up
    return () => window.removeEventListener('focus', handleFocus);

In the above code, we listen to the focus event on the window object and use the focusManager.setFocused() method to inform React Query that the application is now in focus. This is a straightforward yet effective way to ensure that your app fetches the most up-to-date data when it comes into focus, enhancing the overall user experience. However, it is essential to remove the event listener using a clean-up function to prevent memory leaks and potential performance issues.

A common mistake is configuring the focusManager to refetch data too aggressively. This can lead to unnecessary network requests and data fetching, which might degrade the performance of your application. It is best to approach this by adjusting the staleTime and cacheTime configurations for your queries. Opting for a longer staleTime can reduce the frequency of refetches upon refocusing, balancing between data freshness and performance.

import { useQuery } from 'react-query';

const fetchData = async () => {
    const response = await fetch('');
    return response.json();

const useCustomQuery = () => {
    return useQuery('data', fetchData, { staleTime: 5 * 60 * 1000 }); // Data is considered fresh for 5 minutes

In this example, staleTime is set to 5 minutes, which means the data won't be refetched on focus if it was fetched less than 5 minutes ago. This strategy can significantly reduce the number of network requests, especially in applications frequently losing and gaining focus.

In summary, effectively integrating focusManager with React Query involves registering and correctly handling focus events, efficiently managing network requests based on your application's specific needs, and making judicious use of React Query's configuration options to balance performance with the user experience. These practices reduce the risk of over-fetching while ensuring that users have the most current data when they need it.

Leveraging onlineManager for Network State Awareness

React Query's onlineManager plays a crucial role in modern React applications by managing network state changes efficiently. It provides an elegant solution to reduce unnecessary data fetching in offline scenarios. Through the use of onlineManager, developers can leverage its capabilities to pause query refetches when a user's device goes offline, and resume these refetches once the device regains network connectivity. This functionality not only enhances the application's performance by reducing the load on both the client and server but also improves the user experience by fetching fresh data as soon as the application goes back online.

Implementing onlineManager is straightforward. It involves setting an event listener that monitors changes in the network state. This event listener can be configured to update the application's state in response to changes in online status. The online status can be determined using navigator-based APIs or more sophisticated methods in hybrid applications like React Native, where network information can be accessed through third-party plugins like NetInfo.

Here's a simplified example of how to use onlineManager within a React component:

import { useEffect } from 'react';
import { onlineManager } from 'react-query';

function useNetworkAwareness() {
  useEffect(() => {
    const unsubscribe = onlineManager.setEventListener(setOnline => {
      // Logic to handle online status change
      return () => {
        // Cleanup or additional logic

    return unsubscribe; // Cleanup on component unmount
  }, []);

In this code snippet, onlineManager.setEventListener() is used to subscribe to online status changes. The callback provided to setEventListener can execute any logic required to handle the change in network status efficiently, such as pausing or resuming data fetching or even displaying offline indicators within the application.

Handling edge cases is another important aspect when leveraging onlineManager. For example, ensuring the application degrades gracefully in offline scenarios involves providing cached data or meaningful feedback to the user rather than just failing silently. React Query's caching mechanisms work hand in hand with onlineManager to serve stale data when offline and automatically refetch when the application goes online again, ensuring data consistency throughout the application without manual intervention.

In conclusion, by efficiently managing network state changes with onlineManager, developers can create more resilient and user-friendly React applications. This approach not only conserves bandwidth and reduces server load during offline periods but also ensures that users always have access to the most up-to-date information. Careful implementation and consideration of edge cases are necessary to fully leverage the benefits of onlineManager and provide a seamless offline experience.

Combining focusManager and onlineManager: Real-World Scenarios

In real-world applications, effective data synchronization is crucial for maintaining a seamless user experience, especially when dealing with fluctuating network conditions. Combining focusManager and onlineManager from React Query offers a robust solution for managing data fetching in response to changes in focus and network status. Consider a scenario where a user, while navigating through a mobile app, experiences intermittent internet connectivity. By leveraging onlineManager, the app can detect when the network state changes from offline to online and automatically trigger a refetch of the data that was missed during the offline period. This ensures that the user always has access to the most current information without manual intervention.

However, network status is only one part of the equation. The user's interaction with the application—such as when it moves into or out of focus—is equally significant. This is where focusManager comes into play. Imagine the user switches to a different app and then returns after some time. On resumption, focusManager detects the app coming back into focus and works in concert with onlineManager to check if there are any updates missed. This is particularly useful in scenarios where the application is left running in the background and the device regains connectivity after a period of being offline.

The sophistication lies in orchestrating these two managers to balance immediacy and efficiency in data fetching without overwhelming the network or the server. An optimal strategy could involve setting up focusManager to trigger a soft refresh of data that checks for updates without necessarily fetching everything anew, while onlineManager could prioritize fetching critical data that has a higher likelihood of having been updated during the offline period. This dual approach ensures that, upon regaining focus or connectivity, the app smartly updates itself with minimal latency, enhancing user satisfaction.

In implementing these strategies, common coding mistakes to avoid include overly aggressive data fetching upon every minor change in focus or network state. Such an approach can lead to unnecessary bandwidth consumption and degraded app performance. A more refined strategy employs debounce techniques or sets a minimal interval between fetches, ensuring that the app does not refetch data too frequently, which might annoy the user and lead to data overload.

In essence, the combined use of focusManager and onlineManager provides a framework for developers to implement sophisticated data synchronization strategies that respond to real-world user behavior and network conditions. This symbiotic relationship not only optimizes application performance but also significantly improves the user experience by ensuring that data is always up to date, yet fetched in a way that is considerate of device limitations and network constraints. Thought-provoking questions for developers could include: How might one further optimize the interplay between focus and online state changes for bulk data synchronization? Or, what additional checks could be integrated to intelligently predict when a refetch is genuinely beneficial vs. when it's potentially redundant?

Common Pitfalls and Best Practices in Managing Focus and Online State

One common pitfall when using React Query's focusManager and onlineManager is overlooking the necessity of an appropriately balanced configuration that respects the user's device and network conditions. For instance, aggressively configuring focusManager to trigger refetches on every focus change without considering the staleTime of queries can lead to unnecessary network requests, adversely impacting both the application's performance and the user experience. A more prudent approach involves adjusting staleTime to a sensible value, ensuring data is only refetched when genuinely deemed stale. This adjustment helps reduce the number of refetches, conserving bandwidth, and improving overall app responsiveness.

Similarly, incorrect handling of onlineManager can also introduce issues, particularly when developers assume its default behavior aligns with all scenarios of their application's network requirements. A common mistake is not customizing the online detection logic for environments where the straightforward use of navigator.onLine or similar mechanisms might not accurately reflect the app's ability to reach the backend services. Correctly implementing custom logic to determine connectivity, such as considering additional conditions or using more sophisticated methods like sending a test request to an endpoint, can significantly enhance the accuracy of online state management.

Moreover, failing to remove event listeners or not using the provided hooks correctly can lead to memory leaks and other unintended side effects. For instance, neglecting to remove a network change event listener when a component unmounts will keep the callback in memory, potentially triggering updates to unmounted components. A best practice is to always ensure clean-up is performed in useEffect hook return functions, which act as the component's componentWillUnmount lifecycle method.

Another oversight is not leveraging these managers to their full potential to improve user experience. For example, intelligently combining focusManager and onlineManager can enable an application to prioritize critical data fetching when coming back online while deferring less important updates until the app is focused by the user. This strategic fetching reduces load times and makes the app feel more responsive.

Lastly, it invites developers to ponder, "Are there areas in my application where leveraging focusManager and onlineManager could reduce unnecessary data fetching and enhance user experience?" Reflecting on this can lead to insights on optimizing data synchronization and fetching strategies, making applications more efficient and pleasant to use. Thoughtfully integrating these features, coupled with a deep understanding of their nuances, can empower developers to craft superior React applications that intelligently manage data fetching based on focus and connectivity, thereby maximizing performance and user satisfaction.


React Query's focusManager and onlineManager are essential tools for managing data freshness and application responsiveness in React applications. The focusManager triggers data fetching when the application comes into focus, ensuring users always interact with the latest data. The onlineManager monitors network state changes and refetches data once the device regains internet connectivity. These tools streamline the process of ensuring data freshness and responsiveness and contribute to optimizing application performance. A challenging task for developers is to intelligently combine focusManager and onlineManager to prioritize critical data fetching and minimize unnecessary network requests, enhancing the user experience and application efficiency.

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