Deploying a Svelte App

Svelte is a radically different approach to building user interfaces with a compiler that converts declarative components into efficient imperative code. Unlike frameworks that run in the browser, Svelte shifts work to the build step, producing vanilla JavaScript that directly manipulates the DOM. This results in smaller bundle sizes, faster performance, and simpler mental models for developers. Svelte’s reactive statements ($:) make managing component state intuitive and natural, while its scoped styles prevent CSS conflicts. Whether you’re building interactive dashboards, real-time applications, or complex single-page applications, Svelte provides an elegant, performant solution that feels refreshing compared to traditional frameworks.

This comprehensive guide walks through deploying a Svelte application to Klutch.sh using either Nixpacks (automatic zero-configuration deployment) or a Dockerfile (manual container control). You’ll learn how to set up a Svelte project, create and compose components, manage reactive state, work with stores, integrate APIs, optimize builds, configure environment variables, implement security best practices, set up monitoring, configure custom domains, and troubleshoot common issues. By the end of this guide, you’ll have a production-ready Svelte application running on Klutch.sh’s global infrastructure with automatic HTTPS, optimized performance, and reliable hosting.

Prerequisites

• Node.js & npm (version 16+, required) – Download Node.js
• Git installed locally and a GitHub account (Klutch.sh uses GitHub as the only git source)
• Klutch.sh account with access to the dashboard at klutch.sh/app
• Basic knowledge of JavaScript, HTML, and CSS
• Text editor or IDE for code editing (VS Code recommended)

---

Getting Started: Create a Svelte App

1. Create a New Svelte Project

Create a new Svelte application using the official template with SvelteKit:

npm create svelte@latest my-svelte-app
cd my-svelte-app
npm install

When prompted, choose the following options for a standard web app:

• Skeleton project
• TypeScript (optional)
• ESLint and Prettier (recommended)

2. Project Structure

A typical Svelte application structure looks like:

my-svelte-app/
├── src/
│   ├── lib/
│   │   ├── components/
│   │   │   ├── Header.svelte
│   │   │   ├── Footer.svelte
│   │   │   ├── Counter.svelte
│   │   │   ├── Card.svelte
│   │   │   └── Button.svelte
│   │   ├── stores/
│   │   │   ├── auth.js
│   │   │   ├── theme.js
│   │   │   └── user.js
│   │   └── utils/
│   │       ├── api.js
│   │       ├── formatting.js
│   │       └── validation.js
│   ├── routes/
│   │   ├── +page.svelte
│   │   ├── +layout.svelte
│   │   ├── about/
│   │   │   └── +page.svelte
│   │   └── dashboard/
│   │       └── +page.svelte
│   ├── app.css
│   └── app.html
├── static/
│   ├── favicon.png
│   └── logo.png
├── .env.example
├── package.json
├── svelte.config.js
├── vite.config.js
├── README.md
└── Dockerfile

3. Install and Run Locally

Install dependencies and start the development server:

npm install
npm run dev

Your Svelte app will be available at http://localhost:5173. The development server provides hot module replacement (HMR) for instant updates as you code.

4. Create Your First Component

Create src/lib/components/Header.svelte:

<script>
  export let title = 'My Svelte App';
</script>

<header>
  <div class="container">
    <h1>{title}</h1>
    <p>Deployed on Klutch.sh</p>
  </div>
</header>

<style>
  header {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    padding: 2rem;
    text-align: center;
    margin-bottom: 2rem;
  }

  h1 {
    margin: 0;
    font-size: 2.5rem;
  }

  p {
    margin: 0.5rem 0 0;
    font-size: 1.1rem;
  }

  .container {
    max-width: 1200px;
    margin: 0 auto;
  }
</style>

5. Create a Counter Component with Reactive Statements

Create src/lib/components/Counter.svelte:

<script>
  let count = 0;
  let history = [];

  // Reactive statement - runs whenever count changes
  $: if (count !== 0) {
    history = [...history, count];
  }

  function increment() {
    count += 1;
  }

  function decrement() {
    count -= 1;
  }

  function reset() {
    count = 0;
    history = [];
  }
</script>

<div class="counter">
  <h2>Counter Demo</h2>
  <div class="counter-display">{count}</div>

  <div class="counter-buttons">
    <button on:click={increment} class="btn btn-success">
      Increment
    </button>
    <button on:click={decrement} class="btn btn-danger">
      Decrement
    </button>
    <button on:click={reset} class="btn btn-secondary">
      Reset
    </button>
  </div>

  {#if history.length > 0}
    <div class="history">
      <h3>History</h3>
      <p>{history.join(', ')}</p>
    </div>
  {/if}
</div>

<style>
  .counter {
    padding: 2rem;
    border: 1px solid #ddd;
    border-radius: 8px;
    text-align: center;
    margin-bottom: 2rem;
    background: #f9f9f9;
  }

  .counter-display {
    font-size: 3rem;
    font-weight: bold;
    color: #667eea;
    margin: 1rem 0;
  }

  .counter-buttons {
    display: flex;
    gap: 1rem;
    justify-content: center;
    margin: 1.5rem 0;
    flex-wrap: wrap;
  }

  .btn {
    padding: 0.75rem 1.5rem;
    border: none;
    border-radius: 4px;
    cursor: pointer;
    font-size: 1rem;
    transition: opacity 0.3s ease;
  }

  .btn:hover {
    opacity: 0.8;
  }

  .btn-success {
    background-color: #27ae60;
    color: white;
  }

  .btn-danger {
    background-color: #e74c3c;
    color: white;
  }

  .btn-secondary {
    background-color: #95a5a6;
    color: white;
  }

  .history {
    margin-top: 1.5rem;
    padding-top: 1.5rem;
    border-top: 1px solid #ddd;
  }

  .history h3 {
    margin-top: 0;
  }
</style>

6. Create a Svelte Store

Create src/lib/stores/user.js:

import { writable } from 'svelte/store';

export const user = writable(null);
export const isAuthenticated = writable(false);
export const loading = writable(false);

export async function login(email, password) {
  loading.set(true);
  try {
    const response = await fetch('/api/login', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ email, password })
    });
    const data = await response.json();
    if (response.ok) {
      user.set(data.user);
      isAuthenticated.set(true);
      localStorage.setItem('token', data.token);
    }
  } catch (error) {
    console.error('Login failed:', error);
  } finally {
    loading.set(false);
  }
}

export function logout() {
  user.set(null);
  isAuthenticated.set(false);
  localStorage.removeItem('token');
}

7. Create API Utilities

Create src/lib/utils/api.js:

const API_BASE_URL = import.meta.env.VITE_API_URL || 'http://localhost:3000';

export const api = {
  get: async (endpoint) => {
    const response = await fetch(`${API_BASE_URL}${endpoint}`, {
      headers: {
        'Content-Type': 'application/json',
        'Authorization': `Bearer ${localStorage.getItem('token') || ''}`
      }
    });
    if (!response.ok) throw new Error(`API error: ${response.status}`);
    return response.json();
  },

  post: async (endpoint, data) => {
    const response = await fetch(`${API_BASE_URL}${endpoint}`, {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'Authorization': `Bearer ${localStorage.getItem('token') || ''}`
      },
      body: JSON.stringify(data)
    });
    if (!response.ok) throw new Error(`API error: ${response.status}`);
    return response.json();
  },

  put: async (endpoint, data) => {
    const response = await fetch(`${API_BASE_URL}${endpoint}`, {
      method: 'PUT',
      headers: {
        'Content-Type': 'application/json',
        'Authorization': `Bearer ${localStorage.getItem('token') || ''}`
      },
      body: JSON.stringify(data)
    });
    if (!response.ok) throw new Error(`API error: ${response.status}`);
    return response.json();
  },

  delete: async (endpoint) => {
    const response = await fetch(`${API_BASE_URL}${endpoint}`, {
      method: 'DELETE',
      headers: {
        'Authorization': `Bearer ${localStorage.getItem('token') || ''}`
      }
    });
    if (!response.ok) throw new Error(`API error: ${response.status}`);
    return response.json();
  }
};

8. Create a Layout Component

Create src/routes/+layout.svelte:

<script>
  import Header from '$lib/components/Header.svelte';
  import Footer from '$lib/components/Footer.svelte';
  import '../app.css';
</script>

<Header title="Svelte on Klutch.sh" />

<nav class="navbar">
  <div class="container">
    <a href="/">Home</a>
    <a href="/about">About</a>
    <a href="/dashboard">Dashboard</a>
  </div>
</nav>

<main>
  <slot />
</main>

<Footer />

<style>
  :global(body) {
    margin: 0;
    padding: 0;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    line-height: 1.6;
    color: #333;
  }

  :global(.container) {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 1rem;
  }

  :global(main) {
    flex: 1;
    padding: 2rem 1rem;
  }

  .navbar {
    background-color: #f5f5f5;
    border-bottom: 1px solid #ddd;
    padding: 1rem 0;
    margin-bottom: 2rem;
  }

  .navbar :global(.container) {
    display: flex;
    gap: 2rem;
  }

  .navbar a {
    text-decoration: none;
    color: #333;
    font-weight: 500;
    transition: color 0.3s ease;
  }

  .navbar a:hover {
    color: #667eea;
  }
</style>

9. Create Home Page

Create src/routes/+page.svelte:

<script>
  import Counter from '$lib/components/Counter.svelte';
</script>

<svelte:head>
  <title>Home - Svelte on Klutch.sh</title>
</svelte:head>

<div class="container">
  <h2>Welcome to Svelte</h2>
  <p>Svelte is a radical new approach to building user interfaces.</p>

  <ul class="features">
    <li>⚡ Lighter, faster, and simpler</li>
    <li>✨ Write less code with reactive statements</li>
    <li>🎯 Scoped styles by default</li>
    <li>🚀 True reactivity with less boilerplate</li>
  </ul>

  <section class="demo-section">
    <h2>Interactive Demo</h2>
    <Counter />
  </section>
</div>

<style>
  :global(.container) {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 1rem;
  }

  h2 {
    color: #333;
  }

  .features {
    list-style: none;
    padding: 0;
  }

  .features li {
    padding: 0.5rem 0;
    font-size: 1.1rem;
  }

  .demo-section {
    margin-top: 3rem;
  }
</style>

10. Create Environment Variables

Create .env.example:

VITE_API_URL=http://localhost:3000
VITE_APP_NAME=My Svelte App
VITE_ANALYTICS_ID=
VITE_ENABLE_DEBUG=false

11. Configure Build

Update svelte.config.js:

import adapter from '@sveltejs/adapter-auto';

export default {
  kit: {
    adapter: adapter(),
    env: {
      dir: '.',
      prefix: 'VITE_'
    }
  }
};

12. Build Optimization

Create a production build with optimizations:

npm run build

This creates an optimized, minified bundle in the build/ directory ready for production deployment.

13. Test Production Build Locally

Serve the production build locally:

npm install -g http-server
http-server build -p 3000

Visit http://localhost:3000 to test your production build.

---

Local Production Build Test

Before deploying, test your application in a production-like environment:

# Build for production
npm run build

# Serve the production build
http-server build -p 3000 --gzip

Verify that:

• All pages load correctly
• Interactive components work as expected
• API calls function properly
• Performance metrics are acceptable
• No console errors appear in DevTools
• Mobile responsiveness is correct
• Navigation works smoothly
• Stores maintain state properly

---

Deploying with Nixpacks

Nixpacks automatically detects your Svelte application and configures build and runtime environments without requiring a Dockerfile. This is the simplest deployment method for Svelte apps.

Prerequisites for Nixpacks Deployment

• Your Svelte project pushed to a GitHub repository
• Valid package.json with build and start scripts
• No Dockerfile in the repository root (if one exists, Klutch.sh will use Docker instead)

Steps to Deploy with Nixpacks

1. Push Your Svelte App to GitHub

   Initialize and push your project to GitHub:

   git init
   git add .
   git commit -m "Initial Svelte app"
   git branch -M main
   git remote add origin git@github.com:YOUR_USERNAME/YOUR_REPO.git
   git push -u origin main

2. Log In to Klutch.sh Dashboard

   Go to klutch.sh/app and sign in with your GitHub account.

3. Create a Project

   Navigate to the Projects section and create a new project for your Svelte app.

4. Create an App

   Click “Create App” and select your GitHub repository.

5. Select the Branch

   Choose the branch you want to deploy (typically main).

6. Configure Traffic Type

   Select HTTP as the traffic type for Svelte (a web application serving HTML/CSS/JS).

7. Set the Internal Port

   Set the internal port to 3000 – this is the port where Nixpacks will serve your Svelte app using a production HTTP server.

8. Add Environment Variables (Optional)

   Add any environment variables your Svelte app requires:

   VITE_API_URL=https://api.example.com
   VITE_APP_NAME=My Svelte App
   VITE_ANALYTICS_ID=your-analytics-id
   NODE_ENV=production

   If you need to customize the Nixpacks build or start command, use these environment variables:

   • BUILD_COMMAND: Override the default build command (e.g., npm run build)
   • START_COMMAND: Override the default start command (e.g., http-server build -p 3000)
9. Configure Compute Resources

   Select your region, compute size, and number of instances based on expected traffic.

10. Deploy

    Click “Create” to start the deployment. Nixpacks will automatically build and deploy your Svelte app. Your app will be available at a URL like https://example-app.klutch.sh.

---

Deploying with Docker

For more control over your deployment environment, you can use a Dockerfile. Klutch.sh automatically detects a Dockerfile in your repository root and uses it for deployment.

Creating a Dockerfile for Svelte

Create a Dockerfile in the root of your Svelte project:

# === Build stage ===
FROM node:20-alpine AS builder

WORKDIR /app

COPY package*.json ./
RUN npm install

COPY . .
RUN npm run build


# === Production stage ===
FROM nginx:alpine

COPY --from=builder /app/build /usr/share/nginx/html

# Configure Nginx for Svelte SPA
RUN echo 'server { \
  listen 80; \
  server_name _; \
  root /usr/share/nginx/html; \
  index index.html index.htm; \
  \
  location / { \
    try_files $uri $uri/ /index.html; \
  } \
  \
  location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2|ttf|eot)$ { \
    expires 1y; \
    add_header Cache-Control "public, immutable"; \
  } \
}' > /etc/nginx/conf.d/default.conf

EXPOSE 80

CMD ["nginx", "-g", "daemon off;"]

Alternative Dockerfile Using Node.js http-server

For a lightweight alternative using Node.js http-server:

FROM node:20-alpine

WORKDIR /app

COPY package*.json ./
RUN npm install

COPY . .
RUN npm run build

ENV PORT=3000
EXPOSE 3000

CMD ["npx", "http-server", "build", "-p", "3000", "--gzip"]

Dockerfile Notes

• Build stage: Installs dependencies and builds your Svelte app.
• Production stage: Uses Nginx (recommended for SPAs) or http-server to serve your static files.
• Port: The PORT environment variable is set to 3000 for http-server or 80 for Nginx.
• Multi-stage build: Reduces final image size by excluding Node.js and build tools from the runtime container.
• SPA routing: The Nginx configuration includes try_files $uri $uri/ /index.html for proper client-side routing.
• Caching headers: Nginx configuration includes long-term caching for static assets.

Steps to Deploy with Docker

1. Create a Dockerfile

   Add the Dockerfile (shown above) to the root of your Svelte repository.

2. Test Locally (Optional)

   Build and test the Docker image locally:

   docker build -t svelte-app:latest .
   docker run -p 3000:80 svelte-app:latest

   Visit http://localhost:3000 to verify.

3. Push to GitHub

   Commit and push the Dockerfile and your code:

   git add Dockerfile
   git commit -m "Add Dockerfile for production deployment"
   git push origin main

4. Create an App in Klutch.sh

   Go to klutch.sh/app, navigate to “Create App”, and select your repository.

5. Configure the App
   • Traffic Type: Select HTTP
   • Internal Port: Set to 80 (Nginx) or 3000 (http-server)
   • Environment Variables: Add any required runtime variables
6. Deploy

   Klutch.sh automatically detects the Dockerfile and uses it to build and deploy your app. Your app will be available at https://example-app.klutch.sh.

---

Environment Variables

Define environment variables in the Klutch.sh dashboard for production configuration:

VITE_API_URL=https://api.example.com
VITE_APP_NAME=My Svelte App
VITE_ANALYTICS_ID=your-analytics-id
NODE_ENV=production

Accessing Environment Variables

Access environment variables in your Svelte app through import.meta.env:

// In your components or utilities
const apiUrl = import.meta.env.VITE_API_URL || 'http://localhost:3000';
const appName = import.meta.env.VITE_APP_NAME || 'My App';
const analyticsId = import.meta.env.VITE_ANALYTICS_ID || '';
const isDev = import.meta.env.DEV;
const isProd = import.meta.env.PROD;

// Usage in component
<h1>{appName}</h1>
<p>Environment: {isProd ? 'production' : 'development'}</p>

Building with Custom Environment Variables

Ensure environment variables are prefixed with VITE_ to be available in the browser:

VITE_API_URL=https://api.example.com npm run build

---

Persistent Storage

If your Svelte app generates files, caches data, or needs to store user-generated content on the server, you can use persistent volumes in Klutch.sh.

Adding Persistent Volumes

1. In the Klutch.sh dashboard, go to your app’s Volumes section.
2. Click Add Volume.
3. Set the mount path (e.g., /data, /uploads, /cache).
4. Set the size (e.g., 1 GiB, 5 GiB).
5. Save and redeploy your app.

Example: Using localStorage with Server Sync

// Sync browser localStorage with server
function syncDataToServer() {
  const userData = localStorage.getItem('userData');
  if (userData) {
    api.post('/api/user-data', JSON.parse(userData))
      .then(() => console.log('Data synced'))
      .catch(err => console.error('Sync failed:', err));
  }
}

// In your layout component
<script>
  import { onMount } from 'svelte';

  onMount(() => {
    window.addEventListener('beforeunload', syncDataToServer);
    return () => window.removeEventListener('beforeunload', syncDataToServer);
  });
</script>

---

Security Best Practices

1. HTTPS/SSL Enforcement

Klutch.sh automatically provides HTTPS for all deployed apps. All traffic is encrypted and secure by default.

2. Content Security Policy

Implement CSP headers to protect against XSS attacks. Configure in Nginx:

add_header Content-Security-Policy "default-src 'self'; script-src 'self' 'unsafe-inline'; style-src 'self' 'unsafe-inline'; img-src 'self' data: https:;" always;

3. Protect Against CSRF

Use CSRF tokens for forms and API requests:

// Get CSRF token from meta tag or local storage
const csrfToken = document.querySelector('meta[name="csrf-token"]')?.content
  || localStorage.getItem('csrf-token');

// Add to API requests
export const api = {
  post: async (endpoint, data) => {
    const response = await fetch(`${API_BASE_URL}${endpoint}`, {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'X-CSRF-Token': csrfToken || ''
      },
      body: JSON.stringify(data)
    });
    return response.json();
  }
};

4. Input Validation and Sanitization

Always validate and sanitize user input:

// Validate email
function validateEmail(email) {
  const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
  return emailRegex.test(email);
}

// Sanitize HTML input
function sanitizeInput(input) {
  const div = document.createElement('div');
  div.textContent = input;
  return div.innerHTML;
}

Usage in component:

<script>
  let email = '';
  let error = '';

  function handleSubmit() {
    if (!validateEmail(email)) {
      error = 'Invalid email address';
      return;
    }
    // Submit form
  }
</script>

<form on:submit|preventDefault={handleSubmit}>
  <input type="email" bind:value={email} required />
  {#if error}
    <p class="error">{error}</p>
  {/if}
  <button type="submit">Submit</button>
</form>

<style>
  .error {
    color: red;
  }
</style>

5. Secure API Communication

Always use HTTPS for API calls and include authentication tokens:

export const api = {
  baseURL: 'https://api.example.com', // Always HTTPS in production

  request: async (method, endpoint, data) => {
    const token = localStorage.getItem('authToken');
    const response = await fetch(`${api.baseURL}${endpoint}`, {
      method,
      headers: {
        'Content-Type': 'application/json',
        'Authorization': token ? `Bearer ${token}` : ''
      },
      body: data ? JSON.stringify(data) : null
    });

    if (response.status === 401) {
      // Handle unauthorized - redirect to login
      window.location.href = '/login';
    }

    return response.json();
  }
};

6. Environment Variable Security

Never commit sensitive data to git. Use environment variables:

// ✗ WRONG - Don't hardcode secrets
const apiKey = 'sk_live_abc123...';

// ✓ CORRECT - Use environment variables
const apiKey = import.meta.env.VITE_API_KEY;

// Never expose secrets in client-side code
// For sensitive operations, call a backend API instead

7. Dependency Security

Keep dependencies updated and audit for vulnerabilities:

npm outdated
npm audit
npm audit fix
npm update

---

Monitoring and Logging

Performance Monitoring

Monitor Svelte app performance using Web Vitals:

import { getCLS, getFID, getFCP, getLCP, getTTFB } from 'web-vitals';

function sendToAnalytics(metric) {
  if (import.meta.env.PROD) {
    fetch('/api/metrics', {
      method: 'POST',
      body: JSON.stringify({
        name: metric.name,
        value: metric.value
      })
    });
  }
}

getCLS(sendToAnalytics);
getFID(sendToAnalytics);
getFCP(sendToAnalytics);
getLCP(sendToAnalytics);
getTTFB(sendToAnalytics);

Error Tracking

Implement global error handling:

export function setupErrorTracking() {
  window.addEventListener('error', (event) => {
    console.error('Global error:', event.error);

    if (import.meta.env.PROD) {
      api.post('/api/errors', {
        message: event.message,
        stack: event.error?.stack,
        url: window.location.href,
        timestamp: new Date().toISOString()
      });
    }
  });

  window.addEventListener('unhandledrejection', (event) => {
    console.error('Unhandled promise rejection:', event.reason);

    if (import.meta.env.PROD) {
      api.post('/api/errors', {
        message: event.reason?.message,
        stack: event.reason?.stack,
        type: 'unhandledRejection',
        url: window.location.href,
        timestamp: new Date().toISOString()
      });
    }
  });
}

Analytics Integration

Add analytics tracking to monitor user behavior:

export function useAnalytics() {
  // Google Analytics
  window.gtag?.('config', 'GA_ID', {
    page_path: window.location.pathname,
    page_title: document.title
  });

  // Track custom events
  window.trackEvent = (eventName, eventData) => {
    window.gtag?.('event', eventName, eventData);
  };
}

---

Custom Domains

To use a custom domain with your Klutch.sh-deployed Svelte app:

1. Add the Domain in Klutch.sh

In the Klutch.sh dashboard, go to your app’s settings and add your custom domain (e.g., app.example.com).

2. Update Your DNS Provider

Update your DNS records with the CNAME provided by Klutch.sh:

CNAME: app.example.com → example-app.klutch.sh

3. Update Your Svelte App

Update API endpoints if needed:

// API configuration
export const API_BASE_URL = import.meta.env.VITE_API_URL
  || (window.location.hostname.includes('localhost')
    ? 'http://localhost:3000'
    : 'https://api.example.com');

4. Wait for DNS Propagation

DNS changes can take up to 48 hours to propagate. Verify with:

nslookup app.example.com
# or
dig app.example.com CNAME

Once propagated, your Svelte app will be accessible at your custom domain with automatic HTTPS.

---

Troubleshooting

Issue 1: Build Fails with “Module not found”

Error: Cannot find module 'svelte' or similar

Solutions:

• Run npm install to ensure all dependencies are installed
• Check that package.json includes svelte and @sveltejs/kit
• Delete node_modules and package-lock.json, then run npm install again
• Verify file paths are correct (case-sensitive on Linux)

Issue 2: Routing Not Working

Error: 404 on page refresh or bookmarked URLs

Solutions:

• Ensure Nginx configuration includes try_files $uri $uri/ /index.html; for SPA routing
• Check that your routes are in the src/routes/ directory with correct naming
• Verify the internal port is set correctly in Klutch.sh dashboard
• Test locally with production build: npm run build && http-server build

Issue 3: Environment Variables Not Available

Error: import.meta.env.VITE_API_URL is undefined

Solutions:

• Ensure environment variables are prefixed with VITE_ for browser access
• Rebuild after adding new environment variables
• Check that variables are set in Klutch.sh dashboard (refresh if needed)
• Test locally with .env file: VITE_API_URL=http://localhost:3000 npm run dev
• For Node.js-only variables, use process.env (these won’t work in browser)

Issue 4: API Requests Failing (CORS)

Error: CORS error or 401 Unauthorized

Solutions:

• Ensure API URL is correct (check environment variables)
• Verify CORS headers on backend API server
• Check that authentication token is being sent:

  headers: {
    'Authorization': `Bearer ${localStorage.getItem('authToken')}`
  }

• Use relative URLs if calling same-origin API: /api/users instead of full URL

Issue 5: Performance Issues

Error: Slow initial load or janky animations

Solutions:

• Check bundle size with analysis tools
• Enable code splitting for routes automatically done by SvelteKit
• Optimize images and assets
• Use Svelte’s reactive statements efficiently to avoid excessive updates
• Profile with browser DevTools (Performance tab)

Issue 6: Blank Page on Production

Error: App shows blank page or white screen

Solutions:

• Check browser console for JavaScript errors
• Verify index.html is being served correctly
• Check that Nginx/http-server is configured correctly
• Ensure build completed successfully: check for /build folder
• Test production build locally before deploying
• Clear browser cache (Ctrl+Shift+Delete)

Issue 7: Store Values Not Updating

Error: Svelte store values don’t update in components

Solutions:

• Ensure you’re using the $ prefix to subscribe to stores: $userStore
• Check that store modifications trigger reactivity (avoid mutating arrays/objects directly)
• Use proper assignment or store methods to update values
• Verify stores are imported correctly in components

---

Best Practices

1. Component Organization

Organize components by feature or page:

src/lib/components/
  ├── common/
  │   ├── Header.svelte
  │   ├── Footer.svelte
  │   └── Navigation.svelte
  ├── dashboard/
  │   ├── DashboardLayout.svelte
  │   ├── StatsCard.svelte
  │   └── Chart.svelte
  └── auth/
      ├── LoginForm.svelte
      └── RegisterForm.svelte

2. Use Svelte Stores Effectively

Extract component logic into stores for shared state:

stores/counter.js

import { writable } from 'svelte/store';

function createCounter() {
  const { subscribe, set, update } = writable(0);

  return {
    subscribe,
    increment: () => update(n => n + 1),
    decrement: () => update(n => n - 1),
    reset: () => set(0)
  };
}

export const counter = createCounter();

Usage in component:

<script>
  import { counter } from '$lib/stores/counter.js';
</script>

<p>Count: {$counter}</p>
<button on:click={() => counter.increment()}>+</button>

3. Use Reactive Statements

Leverage Svelte’s $: reactive statements to keep values in sync:

<script>
  let count = 0;

  // Reactive statement - runs whenever count changes
  $: doubled = count * 2;

  $: if (count > 10) {
    console.log('Count is over 10');
  }
</script>

<p>Count: {count}</p>
<p>Doubled: {doubled}</p>

4. Handle Loading and Error States

Always provide feedback during data loading:

<script>
  import { api } from '$lib/utils/api.js';

  let data = null;
  let loading = true;
  let error = null;

  async function fetchData() {
    try {
      data = await api.get('/api/users');
    } catch (err) {
      error = err.message;
    } finally {
      loading = false;
    }
  }
</script>

{#if loading}
  <div>Loading...</div>
{:else if error}
  <div>Error: {error}</div>
{:else if data}
  <ul>
    {#each data as user (user.id)}
      <li>{user.name}</li>
    {/each}
  </ul>
{/if}

5. Use Semantic HTML

Write accessible HTML for better SEO and UX:

<!-- ✓ Good - semantic HTML -->
<article>
  <h2>{title}</h2>
  <p>{content}</p>
</article>

<!-- ✗ Avoid - non-semantic divs -->
<div>
  <div>{title}</div>
  <div>{content}</div>
</div>

6. Scope Styles Properly

Use Svelte’s scoped styles to prevent CSS conflicts:

<div class="card">
  <h3>Title</h3>
  <p>Content</p>
</div>

<!-- Styles are scoped to this component -->
<style>
  .card {
    padding: 1rem;
    border: 1px solid #ddd;
  }

  h3 {
    margin-top: 0;
  }
</style>

7. Test Your Components

Write unit tests for critical components:

import { render } from '@testing-library/svelte';
import Counter from './Counter.svelte';

test('Counter increments', () => {
  const { getByText } = render(Counter);
  const button = getByText('Increment');
  button.click();
  // Assert counter incremented
});

8. Document Your Components

Add comments for clarity:

<!--
  Button component with customizable text and click handler
  @param {string} text - Button text
  @param {function} onClick - Click handler
  @param {string} type - Button type (primary, secondary, danger)
-->
<script>
  export let text = 'Click me';
  export let onClick = () => {};
  export let type = 'primary';
</script>

<button class={type} on:click={onClick}>
  {text}
</button>

9. Monitor Bundle Size

Keep your bundle size optimized with SvelteKit’s automatic code splitting.

10. Keep Dependencies Updated

Regularly update Svelte and dependencies:

npm outdated
npm update
npm audit fix

---

Verifying Your Deployment

After deployment completes:

1. Check the App URL: Visit your app at https://example-app.klutch.sh or your custom domain.
2. Test Interactivity: Click buttons, navigate routes, and submit forms.
3. Check Console: Open F12 and verify no errors appear.
4. Test API Integration: Verify API calls work and return expected data.
5. Check Performance: Use Google PageSpeed Insights to verify performance metrics.
6. Test Responsiveness: Verify mobile, tablet, and desktop layouts work.
7. Monitor Logs: Check the Klutch.sh dashboard logs for any issues.

If your app doesn’t work as expected, review the troubleshooting section and check the Klutch.sh dashboard logs for detailed error messages.

---

External Resources

• Official Svelte Documentation
• SvelteKit Documentation
• Klutch.sh Official Website
• MDN JavaScript Documentation
• Web Performance Best Practices
• Web Security Documentation
• Svelte FAQ

---

Deploying a Svelte app to Klutch.sh is straightforward with Nixpacks for automatic deployment or Docker for custom environments. By following this guide, you’ve learned how to create a Svelte project with SvelteKit, build performant components, manage reactive state effectively, integrate with external APIs, optimize builds, configure environment variables, implement security best practices, set up monitoring, and troubleshoot common issues. Your Svelte application is now running on Klutch.sh’s global infrastructure with automatic HTTPS, optimized performance, and reliable hosting. For additional help or questions, consult the official Svelte documentation or contact Klutch.sh support.