How to Manage State in Svelte Applications with Stores

Managing state in web applications can often feel like a daunting task, especially as your application grows and scales. In Svelte, however, handling state is made simple and efficient through the use of stores. In this article, we will explore what Svelte stores are, how to use them effectively, and best practices for managing state in your Svelte applications.

What Are Svelte Stores?

Svelte stores are a reactive state management system built into the Svelte framework. They provide an easy way to share state across multiple components, allowing you to manage your application's data flow cleanly and efficiently. Stores are designed to be simple, lightweight, and easy to use, which aligns perfectly with Svelte's philosophy of minimalism and performance.

Types of Stores

Svelte offers three types of stores:

1. Writable Stores: The most common type, which allows both reading and writing of values.
2. Readable Stores: These are for values that can only be read but not modified.
3. Derived Stores: These are computed based on other stores, allowing you to create new data based on existing state.

Setting Up a Writable Store

Let's start with a simple example of a writable store. This store can hold a count value that we can increase or decrease based on user interaction.

Step 1: Create a Store

First, create a new file named store.js in your Svelte project:

// store.js
import { writable } from 'svelte/store';

export const count = writable(0);

Step 2: Use the Store in a Component

Now, let’s see how to use this store in a Svelte component. Create a new Svelte component called Counter.svelte:

<!-- Counter.svelte -->
<script>
    import { count } from './store.js';

    function increment() {
        count.update(n => n + 1);
    }

    function decrement() {
        count.update(n => n - 1);
    }
</script>

<h1>Count: {$count}</h1>
<button on:click={increment}>Increment</button>
<button on:click={decrement}>Decrement</button>

Explanation

• Importing the Store: You import the writable store count from store.js.
• Using Reactive Statements: The $count syntax automatically subscribes to the store and updates the UI whenever the store changes.
• Updating the Store: The update method allows you to modify the store’s value in a functional way.

Using Readable Stores

Sometimes, you may want to create a store that is read-only. This is where readable stores come in handy. Let's create a simple example of a readable store that fetches and returns a random joke.

Step 1: Create a Readable Store

Modify store.js to include a readable store:

// store.js
import { writable, readable } from 'svelte/store';

export const count = writable(0);

export const joke = readable('', set => {
    async function fetchJoke() {
        const response = await fetch('https://api.chucknorris.io/jokes/random');
        const data = await response.json();
        set(data.value);
    }

    fetchJoke();

    const interval = setInterval(fetchJoke, 10000); // Fetch a new joke every 10 seconds

    return () => clearInterval(interval); // Cleanup
});

Step 2: Use the Readable Store in a Component

Now, let’s display the joke in another Svelte component named JokeDisplay.svelte:

<!-- JokeDisplay.svelte -->
<script>
    import { joke } from './store.js';
</script>

<h2>Random Joke:</h2>
<p>{$joke}</p>

Explanation

• Creating a Readable Store: The readable function takes a callback that sets the initial value and can also include logic for fetching data.
• Automatic Cleanup: The return function in the readable store cleans up intervals when the component is destroyed.

Derived Stores for Computed State

Derived stores allow you to create new state based on existing stores. This is particularly useful for creating more complex data structures without mutating the original state.

Example of a Derived Store

Let’s create a derived store that computes the double of the count.

// store.js
import { derived } from 'svelte/store';

export const doubleCount = derived(count, $count => $count * 2);

Using the Derived Store

You can use doubleCount in your Counter.svelte component like this:

<!-- Counter.svelte -->
<script>
    import { count, doubleCount } from './store.js';
    // ... increment and decrement functions ...
</script>

<h1>Count: {$count}</h1>
<h2>Double Count: {$doubleCount}</h2>
<button on:click={increment}>Increment</button>
<button on:click={decrement}>Decrement</button>

Best Practices for Managing State with Svelte Stores

• Keep Stores Focused: Each store should represent a single piece of state. This keeps your application modular and easier to manage.
• Use Derived Stores: Whenever you need to compute values based on other stores, use derived stores to encapsulate that logic.
• Avoid Side Effects: Minimize side effects in stores. If you need to perform asynchronous operations, consider doing that in the component rather than in the store itself.
• Keep It Simple: Svelte is designed to be simple. Don’t overcomplicate your state management. Use stores only when necessary.

Conclusion

Svelte stores provide a powerful and intuitive way to manage state in your applications. By understanding writable, readable, and derived stores, you can effectively handle complex state management scenarios while keeping your code clean and maintainable. Whether you're building a simple counter or a complex application, Svelte stores can help streamline your development process. Start incorporating stores into your next Svelte project and experience how they can simplify state management for you!