Скачать или смотреть Understanding Why Your Embedded Component Does Not Rerender in React

Discover the common issue of embedded components not rerendering in React, and learn how to resolve it effectively for improved performance and functionality.
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Why Your Embedded Component Doesn't Rerender in React

When you're working with React, one common dilemma developers often face is figuring out why certain components—especially embedded components—fail to rerender as expected. If you've encountered this issue while developing your app, don’t worry! In this post, we will break down the problem, analyze the mechanics behind component rendering in React, and provide a straightforward solution.

The Scenario

Imagine you have two components: Event and FormField.

Event contains a state called event, which is managed using the useState hook.

The setEvent function updates this state when necessary.

FormField accepts the setEvent function as a prop from the Event component and invokes it during a save operation.

The situation arises when you have a useEffect hook in the Event component. It appears like this:

[[See Video to Reveal this Text or Code Snippet]]

Upon saving, even though the setEvent function is called, the FormField does not get rerendered. This can lead to confusion, especially if you're expecting the user interface to reflect the updated state.

The Explanation

Stable Setter Functions

You may be wondering, "What went wrong?" The root cause often lies in how React handles state updates and renders components.

Stable Identity: The setter function returned by useState, such as setEvent, is stable. This means that its identity (or reference) remains the same across renders.

Shallow Comparison: When React rerenders a component, it performs a shallow comparison of props and state. If the props have not changed, React opts out of rerendering for performance reasons.

In this case, since the props (including setEvent) passed from Event to FormField have not changed their references, React decides that there is no need to rerender FormField.

Key Understanding

Primitives vs. Objects: React’s shallow comparison works well for primitive values (like strings or numbers) but can lead to issues with complex data structures like objects or arrays. If your event is an object and its reference remains unchanged (even if the content inside it changes), React won’t trigger a rerender of dependent components.

What Can You Do?

If you're experiencing issues with embedded components not updating as expected, consider the following approaches:

1. Use Memoization

Consider using React.memo() to control when a functional component should rerender. Memoization can optimize performance, but be careful as it might introduce bugs if relied on without proper understanding.

2. Update State Correctly

Make sure you’re correctly updating the state to create a new reference. Instead of directly mutating the existing state, return a new object or array. For instance:

[[See Video to Reveal this Text or Code Snippet]]

3. Trigger Updates Explicitly

In certain cases, you may want to trigger updates explicitly. For instance, you may force an update when necessary, using strategies like local state management or additional hooks to track changes.

Conclusion

Understanding the inner workings of component rendering in React can save you a lot of headaches, especially with embedded components. The key takeaway is that React optimizes rendering by conducting shallow comparisons, meaning that if the references remain the same, components won’t rerender, even if their content changes. By ensuring correct state updates and utilizing memoization appropriately, you can create a smoother user experience.

Now that you know why your embedded components might not be rerendering, you'll be better equipped to handle state updates and ensure your components perform as expected. Happy coding!