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Discover how to effectively manage store updates in Svelte to prevent unnecessary re-renders. Learn to optimize your component rendering with custom writable stores.
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This video is based on the question https://stackoverflow.com/q/65968913/ asked by the user 'Nicolas SEPTIER' ( https://stackoverflow.com/u/1096783/ ) and on the answer https://stackoverflow.com/a/65969658/ provided by the user 'dummdidumm' ( https://stackoverflow.com/u/10196188/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Avoid Unnecessary Re-renders in Svelte: A Guide to Managing Store Updates

Svelte is one of the most popular frameworks for building user interfaces, and it's known for its efficiency and smooth performance. However, as you dive deeper into Svelte, you may encounter some challenges—one of which is managing re-renders when stores are updated. In this guide, we will explore the problem of unwanted re-renders when calling the update method on a Svelte store and provide a solution to avoid this issue.

The Problem: Unwanted Re-renders

When using Svelte and its stores, you may notice that every time you call the update method, the component renders again, regardless of whether the store's value has actually changed. This can be frustrating because it could lead to unnecessary performance costs in larger applications. For example, in the provided code snippet, clicking the button triggers an update, even though it doesn't change the store's contents.

Example Code

Here’s a simple example illustrating the issue:

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

In the store.js file, the implementation looks like this:

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

Every time the button is clicked, you see a log of 'render' in the console, indicating that the component is re-rendering, even though there is no actual change. This raises the question: is this expected behavior, and how can it be improved?

The Solution: Create a Custom Writable Store

The solution to this problem lies in creating a custom writable store that checks if the store's value has changed before re-rendering the component. By implementing a mechanism to only call set when there’s a change, you can avoid unnecessary re-renders. Here's how to do it:

Implementing Custom Writable Store

You can create a custom writable store as follows:

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

How it Works

Internal Writable Store: The customWritable function initializes an internal writable store using Svelte's writable.

Set Method: It defines a set method that only updates the store value if newVal is different from the current value. This prevents an update (and thus a render) if there’s no change.

Update Method: The update method applies a function to the current value, checks if the updated value differs, and sets it only if it does.

Integrating the Custom Store in Your Svelte Component

To integrate this customWritable store in your Svelte app, replace the default writable store with your new implementation. This simple change can lead to significant improvements in performance by minimizing unnecessary re-renders.

Conclusion

Understanding how state management works in Svelte is essential to building efficient applications. By utilizing custom writable stores, you have the control needed to prevent unnecessary component re-renders. This not only enhances the performance of your application but also results in a smoother user experience.

By applying this strategy, you can effectively manage store updates and ensure that your app behaves more like you expect, similar to the principles of libraries like Redux.

Now, get started with your Svelte projects and implement these techniques for optimal performance!