1. Routing Not Working in SvelteKit

Understanding the Issue

Navigation and dynamic routes may not work as expected, leading to 404 errors or broken links.

Root Causes

• Incorrect file-based routing structure.
• Missing or improperly configured +page.svelte or +page.server.js files.
• Deployment settings not handling dynamic routes correctly.

Fix

Ensure routes are correctly structured in the src/routes/ directory:

src/routes/
  ├── +layout.svelte
  ├── index.svelte
  ├── about/
  │   ├── +page.svelte
  │   ├── +page.server.js

Use use:enhance for client-side navigation:

<a href="/about" use:enhance>About Us</a>

Ensure correct fallback configuration in vite.config.js for SPA mode:

import { sveltekit } from '@sveltejs/kit/vite';
export default {
  plugins: [sveltekit()],
  server: {
    historyApiFallback: true,
  },
};

2. Server-Side Rendering (SSR) Issues

Understanding the Issue

SSR in SvelteKit may fail due to incorrect data fetching, hydration errors, or API request failures.

Root Causes

• Fetching data incorrectly in +page.server.js.
• Using browser-only APIs during SSR.
• Undefined environment variables causing request failures.

Fix

Ensure data is properly fetched in +page.server.js:

export async function load({ fetch }) {
  const response = await fetch('/api/data');
  if (!response.ok) {
    throw new Error('Failed to fetch data');
  }
  return { data: await response.json() };
}

Wrap browser-only code in onMount to prevent SSR errors:

import { onMount } from 'svelte';
onMount(() => {
  console.log('This runs only in the browser');
});

3. Deployment Problems

Understanding the Issue

SvelteKit applications may not work correctly after deployment due to missing configurations or server incompatibility.

Root Causes

• Improperly set adapter for deployment target.
• Static assets not being served correctly.
• Incorrect routing settings in hosting platforms.

Fix

Ensure the correct adapter is installed in svelte.config.js:

import adapter from '@sveltejs/adapter-node';
export default {
  kit: {
    adapter: adapter()
  }
};

For Vercel deployment, use:

npm install @sveltejs/adapter-vercel

Configure static asset serving correctly for platforms like Netlify or Cloudflare.

4. Environment Variables Not Loading

Understanding the Issue

Environment variables may not be accessible inside SvelteKit applications, leading to API call failures.

Root Causes

• Missing .env file or incorrect variable scope.
• Not using $env correctly in server.js.

Fix

Define environment variables in a .env file:

PUBLIC_API_URL=https://api.example.com

Access variables correctly in SvelteKit:

import { PUBLIC_API_URL } from '$env/static/public';

5. API Integration Failing

Understanding the Issue

APIs may return errors or fail to fetch data correctly in SvelteKit applications.

Root Causes

• Incorrect fetch method usage.
• Cross-origin request (CORS) restrictions.

Fix

Ensure correct API requests:

async function fetchData() {
  const res = await fetch('/api/data');
  if (!res.ok) {
    throw new Error('Failed to fetch data');
  }
  return await res.json();
}

For CORS errors, configure the API server to allow cross-origin requests.

Conclusion

SvelteKit is a powerful front-end framework, but troubleshooting routing errors, SSR issues, deployment problems, environment variable misconfigurations, and API failures is crucial for maintaining a smooth development experience. By following best practices in configuration, error handling, and deployment, developers can ensure robust SvelteKit applications.

FAQs

1. Why is routing not working in SvelteKit?

Ensure correct file-based routing structure and configure fallback settings in vite.config.js.

2. How do I fix SSR errors in SvelteKit?

Use +page.server.js for fetching data and wrap browser-only code inside onMount.

3. Why is my SvelteKit app not working after deployment?

Install the correct adapter for the deployment platform and ensure static assets are correctly served.

4. How do I properly use environment variables in SvelteKit?

Define variables in .env and access them using $env/static/public.

5. How do I fix API integration issues in SvelteKit?

Ensure correct fetch implementation and handle CORS settings on the server.