Скачать или смотреть Understanding Reactivity in Svelte: Fixing the Array Update with Tauri Events

Discover how to ensure arrays remain reactive in Svelte when using Tauri events. Learn key techniques and best practices for managing updates in your applications.
---
This video is based on the question https://stackoverflow.com/q/75372369/ asked by the user 'dscham' ( https://stackoverflow.com/u/5994950/ ) and on the answer https://stackoverflow.com/a/75372525/ provided by the user 'Corrl' ( https://stackoverflow.com/u/15388872/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Array in Svelte not reactive from Tauri listen(), even with $:

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Introduction: The Problem with Reactivity in Svelte

Svelte is a powerful framework that allows developers to create reactive applications with ease. One common issue developers face when working with Svelte and Tauri involves maintaining the reactivity of arrays, especially when they need to listen for events and update accordingly. In this post, we'll explore a scenario where an array of messages does not update as expected when new messages are received from a Tauri event. We'll break down the issue and provide a clear solution to ensure that your application behaves as intended.

The Scenario

Imagine you have an application that displays a list of messages in a chat interface. Whenever a new message is sent, you want the application to automatically update the list of messages. You’ve tried following the documentation by leveraging Svelte's reactivity features, but the updates aren’t triggering as expected. The failure to re-render could be linked to the way you've implemented the handling of async calls and events.

Analyzing the Code

Here’s a quick look at the code you've written to manage messages:

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

Recognizing the Issue

The issue here is that the Svelte reactivity system is not recognizing changes to the messages array when it is being used within an asynchronous await block. The key line causing confusion is this one:

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

When this syntax is used, Svelte creates a new variable (sortedMessages) scoped only within the {# await} block. Therefore, it does not reference the reactive sortedMessages that you intended to maintain.

The Solution

To address this problem, we need a slight modification to how we manage the promise resolution in your await block.

Recommended Adjustment

You should change the {:then} line to prevent scoping issues. By replacing {:then sortedMessages} with {:then _}, you can ensure that the original reactive variable sortedMessages is utilized correctly.

Here’s how your code should look after the update:

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

Why This Works

Maintaining Reactivity: By not creating a new variable, sortedMessages continues to react to changes in the messages array. Any time messages is updated, sortedMessages updates as well.

Consistent State Management: This approach retains the self-contained nature of your component while ensuring that it effectively listens for new events and updates the displayed messages.

Conclusion

Keeping arrays reactive in Svelte when dealing with asynchronous actions can be tricky, especially in a setup involving Tauri events. By understanding the scope of your variables and making small adjustments to how you handle promise resolutions, you can ensure smooth updates in your application.

The fix we discussed won't only solve your immediate issue but also provide a better foundation for handling asynchronous data in future applications. Happy coding!