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Learn how to effectively handle changes in SvelteKit state to manage UI updates and animations seamlessly across components.
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This video is based on the question https://stackoverflow.com/q/73675195/ asked by the user 'Tithos' ( https://stackoverflow.com/u/857030/ ) and on the answer https://stackoverflow.com/a/73675363/ provided by the user 'Kutay Güler' ( https://stackoverflow.com/u/19009002/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Detect and React to State Changes in SvelteKit

When working with SvelteKit, you may encounter scenarios where you want to trigger UI changes based on state changes occurring in different components. One such use case is adding a class to a navigation element when an animation in another component ends. In this guide, we'll explore how to achieve this by properly utilizing Svelte's reactive state.

The Problem: Class Management in SvelteKit

Imagine you have two components in your SvelteKit application: a logo component that performs an animation, and a navigation component that should respond to that animation's completion. You want to add a specific class to the navigation element when the logo's animation concludes.

In your current setup, while you do have the logic to update a store when the animation ends, the way you're checking the state in the navigation component isn't functioning as intended. Let’s break down why this happens and how to fix it.

The Current Approach

In your Logo.svelte file, you have implemented an event listener for the animationend event:

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

While this part of your code correctly updates the store when the animation ends, the logic in your Nav.svelte file needs some adjustments.

Issues with the Navigation Component

In your Nav.svelte, you currently check the state like this:

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

Why Doesn't This Work?

Reactive Update: The if block checking $isLogoAnimationEnded runs only once when the component is mounted. This means that it won't reactively update the navigation element when the state changes.

Class Management: Using querySelector complicates your component unnecessarily.

The Solution: Reactive Class Binding

To efficiently respond to changes in the store, you can leverage Svelte's built-in reactivity directly in the markup. Here’s how:

Step 1: Bind Class to the Navigation Element

You should bind the class of the <nav> element directly to the $isLogoAnimationEnded variable like this:

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

Step 2: Include Necessary Imports

Make sure your Nav.svelte file properly imports the store:

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

Final Code Example

Here's what the improved version of your Nav.svelte component would look like:

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

Conclusion

By binding the class of the navigation directly to the state variable, you've streamlined your component and ensured that it reacts to the changes in the animation state. This makes your code cleaner and significantly enhances performance by utilizing Svelte’s reactivity.

Feel free to apply these changes and watch your components seamlessly interact with one another!