Svelte is a modern JavaScript framework that has been gaining popularity for its simplicity and performance. Unlike traditional frameworks like React or Vue, Svelte shifts much of the work to the compile step, which results in faster and more efficient applications. This guide will take you through the essentials of getting started with Svelte, covering everything from setting up your development environment to deploying your first Svelte application.
What is Svelte?

Svelte is a component framework that allows developers to build interactive user interfaces. It stands out because it does not use a virtual DOM.
Instead, it compiles your components to highly efficient imperative code that directly manipulates the DOM. This means smaller bundle sizes and faster runtime performance.
Svelte’s approach simplifies many aspects of web development. It handles reactivity in a straightforward manner, eliminating the need for complex state management solutions.
This makes it an excellent choice for both beginners and experienced developers looking for a more efficient way to build web applications.
Setting Up Your Development Environment
To get started with Svelte, you need to set up your development environment. This involves installing Node.js and npm (Node Package Manager), as Svelte uses these tools to manage dependencies and build your projects.
First, download and install Node.js from the official website. This will also install npm. Once you have Node.js and npm installed, you can verify the installation by running the following commands in your terminal:
node -v
npm -v
These commands should display the installed versions of Node.js and npm, confirming that they are ready to use.
Next, you need to create a new Svelte project. Svelte provides a template to help you get started quickly. Run the following commands to create a new project:
npx degit sveltejs/template svelte-app
cd svelte-app
npm install
The npx degit
command clones the Svelte template repository into a directory named svelte-app
. The cd svelte-app
command changes the current directory to your new project directory, and npm install
installs the necessary dependencies.
After the installation is complete, you can start the development server by running:
npm run dev
This command starts a local development server and opens your new Svelte app in your default web browser. You should see the default Svelte app running, which confirms that your development environment is set up correctly.
Understanding the Basics of Svelte
With your environment ready, it’s time to dive into the basics of Svelte. Svelte applications are built using components. A component in Svelte is a reusable piece of UI that is defined in a .svelte
file. Each component file can contain HTML, CSS, and JavaScript, all in one place.
Here’s a simple example of a Svelte component:
<script>
let name = 'world';
</script>
<style>
h1 {
color: purple;
}
</style>
<h1>Hello {name}!</h1>
This component defines a variable name
and uses it in the HTML to display a greeting. The CSS styles the greeting, and the HTML renders it. This combination of HTML, CSS, and JavaScript in a single file makes it easy to manage and understand your components.
Reactive Declarations
One of Svelte’s most powerful features is its reactivity. Reactive declarations in Svelte are defined using the $:
syntax. This allows you to automatically update values when dependencies change.
For example:
<script>
let count = 0;
$: doubled = count * 2;
</script>
<p>{count} doubled is {doubled}</p>
<button on:click={() => count += 1}>Increment</button>
In this example, the doubled
variable is automatically updated whenever count
changes. This is a simple yet powerful way to handle state changes in your application.
Event Handling
Handling events in Svelte is straightforward. You can listen to events using the on:
directive. For example, the button
element in the previous example listens for click
events and increments the count
variable.
Svelte also provides a way to create custom events, allowing components to communicate with each other effectively. Custom events are dispatched using the createEventDispatcher
function.
Props and Stores
Props in Svelte allow you to pass data from a parent component to a child component. This is similar to how props work in other frameworks. You define props using the export
keyword.
For example:
<!-- ParentComponent.svelte -->
<script>
import ChildComponent from './ChildComponent.svelte';
let message = 'Hello from parent!';
</script>
<ChildComponent {message} />
<!-- ChildComponent.svelte -->
<script>
export let message;
</script>
<p>{message}</p>
In this example, the ParentComponent
passes the message
prop to the ChildComponent
, which then displays it.
Svelte also introduces a concept called stores, which are a way to manage state that can be shared across multiple components. Stores can be writable or readable, and they provide a reactive way to manage state.
Working with Stores
To create a store, you use the writable
function from the svelte/store
module. Here’s an example of a simple writable store:
// store.js
import { writable } from 'svelte/store';
export const count = writable(0);
In a Svelte component, you can subscribe to the store to get its value and react to changes:
<script>
import { count } from './store.js';
</script>
<p>{$count}</p>
<button on:click={() => count.update(n => n + 1)}>Increment</button>
In this example, the count
store’s value is displayed in the paragraph, and the button increments the count when clicked.
Building Complex Components in Svelte
With the basics covered, let’s delve into building more complex components. Svelte’s simplicity and flexibility make it ideal for creating dynamic and interactive applications. We’ll explore how to use Svelte’s features to build components that interact seamlessly.
Component Composition
In Svelte, you can compose components by nesting them within each other. This is a powerful feature that allows you to build complex UIs from simple, reusable components.
For example, let’s create a simple to-do list application. We’ll start with a TodoItem
component that represents an individual to-do item:
<!-- TodoItem.svelte -->
<script>
export let todo;
</script>
<p>{todo.text}</p>
Next, we’ll create a TodoList
component that uses the TodoItem
component to display a list of to-dos:
<!-- TodoList.svelte -->
<script>
import TodoItem from './TodoItem.svelte';
let todos = [
{ id: 1, text: 'Learn Svelte' },
{ id: 2, text: 'Build a Svelte app' },
{ id: 3, text: 'Deploy the app' },
];
</script>
{#each todos as todo (todo.id)}
<TodoItem {todo} />
{/each}
In this example, the TodoList
component maintains an array of to-dos and uses the #each
block to iterate over them, rendering a TodoItem
for each one. This approach allows you to break down your application into smaller, manageable pieces, making it easier to develop and maintain.
Handling Form Inputs
Handling form inputs in Svelte is straightforward, thanks to its reactivity. You can bind input values to variables using the bind:
directive. This creates a two-way binding, automatically updating the variable when the input changes and vice versa.
For example, let’s add a form to our to-do list application to allow users to add new to-dos:
<!-- TodoList.svelte -->
<script>
import TodoItem from './TodoItem.svelte';
let todos = [
{ id: 1, text: 'Learn Svelte' },
{ id: 2, text: 'Build a Svelte app' },
{ id: 3, text: 'Deploy the app' },
];
let newTodoText = '';
function addTodo() {
if (newTodoText.trim()) {
todos = [...todos, { id: todos.length + 1, text: newTodoText }];
newTodoText = '';
}
}
</script>
<input type="text" bind:value={newTodoText} placeholder="New to-do" />
<button on:click={addTodo}>Add To-Do</button>
{#each todos as todo (todo.id)}
<TodoItem {todo} />
{/each}
In this example, the input field is bound to the newTodoText
variable. When the user types in the input field, the newTodoText
variable is automatically updated. The addTodo
function adds a new to-do to the list when the button is clicked.
Lifecycle Methods
Svelte provides lifecycle methods that allow you to run code at specific points in a component’s lifecycle. These methods include onMount
, beforeUpdate
, afterUpdate
, and onDestroy
. They are useful for performing actions such as fetching data, setting up subscriptions, or cleaning up resources.
For example, let’s use the onMount
lifecycle method to fetch data when a component is first rendered:
<!-- TodoList.svelte -->
<script>
import { onMount } from 'svelte';
let todos = [];
onMount(async () => {
const response = await fetch('/api/todos');
todos = await response.json();
});
</script>
{#each todos as todo (todo.id)}
<p>{todo.text}</p>
{/each}
In this example, the onMount
method is used to fetch a list of to-dos from an API when the component is first rendered. The fetched data is then assigned to the todos
variable, and the to-dos are displayed in the component.
Advanced Svelte Features

Beyond the basics, Svelte offers advanced features that enable you to build sophisticated applications with ease. Let’s explore some of these features.
Context API
The Context API in Svelte allows you to pass data and functions between components without prop drilling. This is particularly useful for managing global state or sharing common functionality across multiple components.
To use the Context API, you set a context value in a parent component and retrieve it in a child component. Here’s an example:
<!-- App.svelte -->
<script>
import { setContext } from 'svelte';
import TodoList from './TodoList.svelte';
const user = { name: 'John Doe' };
setContext('user', user);
</script>
<TodoList />
<!-- TodoList.svelte -->
<script>
import { getContext } from 'svelte';
const user = getContext('user');
</script>
<p>User: {user.name}</p>
In this example, the App
component sets a context value for the user, and the TodoList
component retrieves and displays the user’s name.
Transitions and Animations
Svelte includes built-in support for transitions and animations, allowing you to add smooth and interactive effects to your components with minimal effort. You can use the transition
directive to apply transitions to elements when they enter or leave the DOM.
For example, let’s add a fade transition to our to-do items:
<!-- TodoItem.svelte -->
<script>
export let todo;
import { fade } from 'svelte/transition';
</script>
<p transition:fade>{todo.text}</p>
In this example, the fade
transition is applied to the p
element, making it fade in and out when it enters or leaves the DOM.
You can also create custom animations using the animate
directive and the animate
function from the svelte/animate
module. This allows you to create more complex and tailored animations for your components.
Stores and Derived Stores
While we have already touched on stores, let’s delve deeper into derived stores, which allow you to create stores based on other stores. Derived stores automatically update their values when the source stores change, making it easy to create reactive and dependent state.
For example, let’s create a derived store that calculates the number of remaining to-dos in our to-do list application:
// store.js
import { writable, derived } from 'svelte/store';
export const todos = writable([
{ id: 1, text: 'Learn Svelte', completed: false },
{ id: 2, text: 'Build a Svelte app', completed: false },
{ id: 3, text: 'Deploy the app', completed: false },
]);
export const remainingTodos = derived(todos, $todos => $todos.filter(todo => !todo.completed).length);
In this example, the remainingTodos
derived store calculates the number of to-dos that are not completed. You can then use this derived store in your components:
<!-- TodoList.svelte -->
<script>
import { todos, remainingTodos } from './store.js';
</script>
<p>Remaining to-dos: {$remainingTodos}</p>
{#each $todos as todo (todo.id)}
<p>{todo.text}</p>
{/each}
Server-Side Rendering (SSR)
SvelteKit, the official framework for building Svelte applications, supports server-side rendering (SSR). SSR can improve the performance and SEO of your application by rendering the initial HTML on the server and sending it to the client.
To enable SSR in a SvelteKit project, you simply configure the project to use an SSR adapter. Here’s an example of setting up a basic SvelteKit project with SSR:
- Create a new SvelteKit project:
npm init svelte@next my-svelte-app
cd my-svelte-app
npm install
- Configure the project to use an SSR adapter. In the
svelte.config.js
file, import and configure the adapter:
import adapter from '@sveltejs/adapter-node';
export default {
kit: {
target: '#svelte',
adapter: adapter(),
},
};
- Build and start the server:
npm run build
npm run preview
This will generate a server-side rendered version of your Svelte application, which you can then deploy to a Node.js server or any other platform that supports Node.js.
Deploying Your Svelte Application
Once you have built your Svelte application, the next step is to deploy it. There are several ways to deploy Svelte applications, including static site hosts and traditional servers.
Deploying to Vercel
Vercel is a popular platform for deploying front-end applications. It provides a simple and seamless way to deploy Svelte applications.
To deploy your Svelte application to Vercel, follow these steps:
- Install the Vercel CLI:
npm install -g vercel
- Log in to your Vercel account:
vercel login
- Deploy your application:
vercel
The Vercel CLI will guide you through the deployment process, and your Svelte application will be live on the internet in just a few minutes.
Deploying to Netlify
Netlify is another popular platform for deploying static sites and front-end applications. To deploy your Svelte application to Netlify, follow these steps:
- Install the Netlify CLI:
npm install -g netlify-cli
- Log in to your Netlify account:
netlify login
- Create a
netlify.toml
file in your project root with the following configuration:
[build]
command = "npm run build"
publish = "public"
- Deploy your application:
netlify deploy --prod
The Netlify CLI will guide you through the deployment process, and your Svelte application will be live on the internet shortly.
Deploying to Traditional Servers
If you prefer to deploy your Svelte application to a traditional server, you can do so by building your application and serving the static files. Here are the steps:
- Build your Svelte application:
npm run build
- Copy the contents of the
public
directory to your server. - Configure your server to serve the static files. For example, if you’re using an Apache server, you can add the following configuration to your
.htaccess
file:
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^ index.html [QSA,L]
This configuration ensures that all requests are routed to the index.html
file, enabling client-side routing in your Svelte application.
Testing Svelte Applications

Testing is a crucial aspect of any development process. Svelte provides a robust set of tools and libraries to help you write and run tests for your applications. By ensuring that your components work as expected, you can maintain a high level of code quality and prevent bugs from reaching production.
Unit Testing with Jest
Jest is a popular testing framework that can be used to test Svelte components. To get started with Jest, you need to install it along with the Svelte testing library:
npm install --save-dev jest @testing-library/svelte @testing-library/jest-dom
Next, configure Jest by creating a jest.config.js
file in your project root:
module.exports = {
transform: {
'^.+\\.svelte$': 'svelte-jester',
'^.+\\.js$': 'babel-jest',
},
moduleFileExtensions: ['js', 'svelte'],
setupFilesAfterEnv: ['@testing-library/jest-dom/extend-expect'],
};
Here’s an example of a simple test for a Svelte component:
<!-- Hello.svelte -->
<script>
export let name;
</script>
<h1>Hello {name}!</h1>
// Hello.test.js
import { render } from '@testing-library/svelte';
import Hello from './Hello.svelte';
test('it renders with the correct name', () => {
const { getByText } = render(Hello, { name: 'World' });
expect(getByText('Hello World!')).toBeInTheDocument();
});
In this example, we use the render
function from the Svelte testing library to render the Hello
component with the name
prop set to “World”. The test then checks if the rendered output contains the expected text.
End-to-End Testing with Cypress
Cypress is a powerful tool for end-to-end testing, allowing you to test your application in a real browser environment. To set up Cypress for your Svelte project, install it using npm:
npm install --save-dev cypress
Next, create a cypress.json
file in your project root with the following configuration:
{
"baseUrl": "http://localhost:5000"
}
This configuration tells Cypress where to find your running Svelte application. You can now write end-to-end tests in the cypress/integration
folder:
// cypress/integration/todo.spec.js
describe('To-Do App', () => {
it('loads the to-do list', () => {
cy.visit('/');
cy.contains('Learn Svelte');
cy.contains('Build a Svelte app');
cy.contains('Deploy the app');
});
it('adds a new to-do', () => {
cy.visit('/');
cy.get('input[placeholder="New to-do"]').type('Write tests{enter}');
cy.contains('Write tests');
});
});
In this example, Cypress is used to visit the application’s home page and check that the to-do list is displayed correctly. It also tests adding a new to-do item to the list.
SvelteKit: The Svelte Framework

SvelteKit is the official framework for building Svelte applications. It provides a comprehensive set of tools and features to help you build robust, production-ready applications. SvelteKit handles everything from routing to data fetching, making it a powerful choice for any Svelte project.
Setting Up a SvelteKit Project
To get started with SvelteKit, you can create a new project using the following command:
npm init svelte@next my-sveltekit-app
cd my-sveltekit-app
npm install
This command sets up a new SvelteKit project with the necessary dependencies. You can start the development server by running:
npm run dev
File-Based Routing
SvelteKit uses a file-based routing system, where the file structure of your src/routes
directory defines your application’s routes. For example, to create a new page at /about
, you would create a file at src/routes/about.svelte
:
<!-- src/routes/about.svelte -->
<script>
export let name = 'About Us';
</script>
<h1>{name}</h1>
<p>Welcome to the about page!</p>
Loading Data
SvelteKit provides a load
function that you can use to fetch data before rendering a page. This function runs on both the server and the client, making it ideal for fetching data from APIs or databases.
For example, let’s fetch a list of blog posts and display them on a page:
<!-- src/routes/blog/index.svelte -->
<script context="module">
export async function load({ fetch }) {
const response = await fetch('/api/posts');
const posts = await response.json();
return { props: { posts } };
}
</script>
<script>
export let posts;
</script>
<h1>Blog Posts</h1>
<ul>
{#each posts as post}
<li>{post.title}</li>
{/each}
</ul>
Server-Side Rendering
SvelteKit supports server-side rendering (SSR) out of the box. By default, your SvelteKit application is configured for SSR, which means that the initial HTML is rendered on the server and sent to the client. This can improve the performance and SEO of your application.
API Routes
SvelteKit also allows you to create API routes alongside your frontend code. These routes can be used to handle form submissions, fetch data from external APIs, or perform any other server-side logic.
To create an API route, add a .js
file to the src/routes/api
directory. For example, let’s create an API route that returns a list of blog posts:
// src/routes/api/posts.js
export async function get() {
const posts = [
{ id: 1, title: 'First Post' },
{ id: 2, title: 'Second Post' },
];
return {
status: 200,
body: posts,
};
}
You can then fetch data from this API route in your Svelte components:
<!-- src/routes/blog/index.svelte -->
<script context="module">
export async function load({ fetch }) {
const response = await fetch('/api/posts');
const posts = await response.json();
return { props: { posts } };
}
</script>
Performance Optimization
Optimizing the performance of your Svelte applications ensures that they load quickly and run smoothly. Svelte offers several features and best practices to help you achieve optimal performance.
Code Splitting
Code splitting is a technique that splits your application into smaller chunks, which can be loaded on demand. SvelteKit automatically performs code splitting for your application, ensuring that only the necessary code is loaded for each route.
Lazy Loading
Lazy loading allows you to defer loading of components or resources until they are needed. This can significantly reduce the initial load time of your application.
For example, you can use dynamic imports to lazy load a Svelte component:
<script>
let Component;
async function loadComponent() {
const module = await import('./Component.svelte');
Component = module.default;
}
</script>
<button on:click={loadComponent}>Load Component</button>
{#if Component}
<svelte:component this={Component} />
{/if}
In this example, the Component
is only loaded when the button is clicked, reducing the initial load time.
Optimizing Images
Images can be a major contributor to slow load times. To optimize images, you can use responsive images, lazy loading, and modern image formats like WebP.
For example, you can use the picture
element to serve responsive images:
<picture>
<source srcset="image.webp" type="image/webp">
<img src="image.jpg" alt="Description">
</picture>
Using the svelte-preprocess
Module
The svelte-preprocess
module allows you to preprocess your Svelte components, enabling features like TypeScript, SCSS, and PostCSS. Preprocessing can help you write cleaner and more maintainable code, ultimately improving the performance of your application.
To use svelte-preprocess
, install it and configure your svelte.config.js
file:
npm install --save-dev svelte-preprocess
// svelte.config.js
import preprocess from 'svelte-preprocess';
export default {
preprocess: preprocess(),
};
Conclusion
Getting started with Svelte is an exciting journey into modern web development. Svelte’s unique approach to building web applications simplifies many common tasks and offers excellent performance. In this comprehensive guide, we’ve covered the basics of setting up a Svelte project, building components, handling reactivity, using advanced features, testing, optimizing performance, and deploying your application.
As you continue to explore Svelte, you’ll discover even more features and capabilities that make it a powerful tool for building dynamic and efficient web applications. Whether you’re a beginner or an experienced developer, Svelte provides a refreshing and productive development experience.
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