Everything I Wish I Knew Before Migrating My First Vite Project to Next.js

Moving from a Single Page App to the Server Side

Vite has become the gold standard for developer experience (DX) when building modern Single Page Applications (SPAs). It is incredibly fast, lightweight, and gets out of your way. However, as projects grow, requirements often shift toward SEO optimization, faster First Contentful Paint (FCP), and more robust server-side capabilities.

This is usually when the conversation turns to Next.js. While both frameworks use React, the shift from a client-side Vite project to the file-based routing and Server Components of Next.js is not a simple copy-paste job. Here is everything I wish I had known before I made the leap.

1. The Strategy: CSR vs. SSR vs. RSCs

In Vite, everything is Client-Side Rendered (CSR). You send a nearly empty HTML file and a massive bundle of JavaScript to the browser, which then builds the UI.

In Next.js, the default behavior changed significantly with the introduction of the App Router. Every component is a Server Component (RSC) by default. This means they don't have access to useEffect, useState, or browser APIs like window or localStorage.

The Lesson: Don't try to make everything a Server Component on day one. Start by adding the 'use client' directive to your existing Vite components to keep them working as they did before, then slowly refactor for performance later.

2. Routing: From Code to File System

Most Vite projects use react-router-dom. You have a Routes.tsx file where you define paths and map them to components. In Next.js, the filesystem is the router.

• src/app/page.tsx becomes /
• src/app/about/page.tsx becomes /about
• src/app/blog/[slug]/page.tsx handles dynamic routes like /blog/hello-world

You will need to replace Link from react-router-dom with Link from next/link, and useNavigate with useRouter from next/navigation.

3. Dealing with Browser APIs

Because Next.js attempts to pre-render your pages on the server, code that references window or document will crash your build.

In Vite, you never worried about this. In Next.js, you must wrap these calls in a useEffect hook (which only runs on the client) or check if the window object exists:

if (typeof window !== 'undefined') {
  const token = localStorage.getItem('token');
}

4. Automation vs. Manual Labor

Rewriting paths, updating imports, and restructuring your entire folder layout can take days if the project is large. If you are looking to skip the repetitive boilerplate of converting your routing and component structure, tools like ViteToNext.AI can automate the migration of your Vite + React project into a structured Next.js codebase, saving you hours of manual debugging.

5. The Image Component Pitfall

In Vite, you likely used standard <img> tags. While they still work in Next.js, the framework will nudge you toward the next/image component.

This component is powerful—offering automatic resizing, lazy loading, and WebP conversion—but it requires you to define specific widths and heights or use the fill property. If you have hundreds of images, be prepared for some CSS refactoring to accommodate how next/image handles layout.

6. Data Fetching Change of Heart

In your Vite app, you probably used axios or fetch inside a useEffect hook. While you can still do this in Client Components, the "Next.js way" is to fetch data directly in your Server Components using an async function:

export default async function Page() {
  const data = await fetch('https://api.example.com/data');
  const json = await data.json();

  return <div>{json.title}</div>;
}

This eliminates the need for loading states on the client and keeps your API keys secure since the code never reaches the browser.

7. Configuration: From vite.config.ts to next.config.js

Environment variables change too. In Vite, you used IMPORT.META.ENV.VITE_VARIABLE. In Next.js, you use PROCESS.ENV.NEXT_PUBLIC_VARIABLE. Remember that only variables prefixed with NEXT_PUBLIC_ are accessible to the browser; everything else is strictly server-side.

Conclusion

Migrating to Next.js isn't just a change in build tools; it's a change in mindset. You move from thinking about the "Browser" to thinking about the "Request-Response Cycle."

Start small: migrate your project structure first, get it building with 'use client', and then slowly adopt Server Components and the Next.js Image component to reap the full performance benefits of the framework.

Further reading on automating this process: ViteToNext.AI