How to rebuild UI with React Using Next.js, MongoDB, and Replay AI for complex UI Apps

TL;DR: Rebuild complex React UIs faster by using Replay AI to automatically generate working code from video recordings of user flows, integrated with Next.js, MongoDB, and Supabase.

The promise of AI-powered code generation is finally here, but many tools fall short when faced with complex, multi-page UIs. Screenshot-to-code solutions often fail to capture the intent behind user interactions, resulting in brittle and incomplete code. We need a better way to rebuild UI.

That's where Replay comes in. Replay analyzes video recordings of user sessions to understand user behavior and reconstruct functional UIs. Unlike tools that rely on static images, Replay leverages "Behavior-Driven Reconstruction" – treating the video as the source of truth for how the application should work. This approach is especially powerful when combined with technologies like Next.js, MongoDB, and Supabase for building modern web applications.

This article will guide you through the process of rebuilding a UI using Replay, integrating it into a Next.js project with MongoDB for data persistence and Supabase for authentication.

Understanding Behavior-Driven Reconstruction#

Most existing UI reconstruction tools analyze static images. This approach is limited because it only captures the visual appearance of the UI at a specific moment in time. It misses crucial information about user interactions, state transitions, and the overall flow of the application.

Replay takes a different approach. By analyzing video recordings, Replay can understand:

• •Click events and their effects
• •Form submissions and data flow
• •Page transitions and navigation patterns
• •Dynamic content updates based on user input

This "Behavior-Driven Reconstruction" allows Replay to generate code that accurately reflects the intended behavior of the UI, leading to more robust and maintainable applications.

Setting Up Your Development Environment#

Before we dive into using Replay, let's set up our development environment with Next.js, MongoDB, and Supabase.

Step 1: Create a Next.js Project#

If you don't already have a Next.js project, create one using the following command:

bash
npx create-next-app@latest my-replay-app
cd my-replay-app

Choose the default options for TypeScript, ESLint, Tailwind CSS,

directory, App Router, and import alias.

Step 2: Connect to MongoDB#

First, you'll need a MongoDB database. You can use MongoDB Atlas (cloud-based) or a local instance.

💡 Pro Tip: Using environment variables to store your MongoDB connection string is crucial for security.

Install the MongoDB driver:

bash
npm install mongodb

Create a

file in the root of your project and add your MongoDB connection string:

text
MONGODB_URI="mongodb+srv://<username>:<password>@<cluster>.mongodb.net/?retryWrites=true&w=majority"
MONGODB_DB="replay_db"

Replace

, , and with your MongoDB credentials.

Create a file

:

javascript
// lib/mongodb.js
import { MongoClient } from 'mongodb';

const uri = process.env.MONGODB_URI;
const dbName = process.env.MONGODB_DB;

let cachedClient = null;
let cachedDb = null;

if (!uri) {
  throw new Error(
    'Please define the MONGODB_URI environment variable inside .env.local'
  );
}

if (!dbName) {
  throw new Error(
    'Please define the MONGODB_DB environment variable inside .env.local'
  );
}

export async function connectToDatabase() {
  if (cachedClient && cachedDb) {
    return {
      client: cachedClient,
      db: cachedDb,
    };
  }

  const client = await MongoClient.connect(uri);

  const db = await client.db(dbName);

  cachedClient = client;
  cachedDb = db;

  return {
    client: client,
    db: db,
  };
}

This code establishes a connection to your MongoDB database using the provided URI and database name. It also implements connection caching to improve performance.

Step 3: Integrate with Supabase for Authentication#

Supabase provides a simple and scalable authentication solution.

Create a Supabase project at https://supabase.com/.

Install the Supabase client library:

bash
npm install @supabase/supabase-js @supabase/auth-helpers-nextjs @supabase/auth-helpers-react

Configure Supabase in your Next.js application. Add the Supabase URL and anon key to your

file:

text
NEXT_PUBLIC_SUPABASE_URL="YOUR_SUPABASE_URL"
NEXT_PUBLIC_SUPABASE_ANON_KEY="YOUR_SUPABASE_ANON_KEY"

Create a Supabase client instance in

:

javascript
// lib/supabaseClient.js
import { createClient } from '@supabase/supabase-js'

const supabaseUrl = process.env.NEXT_PUBLIC_SUPABASE_URL
const supabaseAnonKey = process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY

export const supabase = createClient(supabaseUrl, supabaseAnonKey)

Now you have a Next.js project connected to both MongoDB and Supabase. This provides a solid foundation for integrating the code generated by Replay.

Rebuilding UI with Replay#

Now that our environment is set up, let's use Replay to rebuild a UI.

Step 1: Record a Video of the UI#

The first step is to record a video of the UI you want to rebuild. This video should demonstrate the key user flows and interactions you want to capture. Be sure to include all relevant pages, forms, and state transitions.

📝 Note: The quality of the video directly impacts the accuracy of the generated code. Ensure the video is clear, stable, and captures all relevant UI elements.

Step 2: Upload the Video to Replay#

Navigate to the Replay platform and upload the video recording. Replay will automatically analyze the video and begin reconstructing the UI.

Step 3: Review and Refine the Generated Code#

Once Replay has finished analyzing the video, it will present you with a set of generated React components. Review these components carefully and make any necessary adjustments.

Replay offers features like:

• •Multi-page generation: Replay automatically detects page transitions and generates separate components for each page.
• •Supabase integration: Replay can automatically generate authentication logic and data fetching hooks using Supabase.
• •Style injection: Replay attempts to infer the styling of the UI and inject CSS or Tailwind CSS classes into the generated components.
• •Product Flow maps: Replay provides visual diagrams of the user flows it has detected, allowing you to quickly understand the structure of the application.

Step 4: Integrate the Code into Your Next.js Project#

Copy the generated React components into your Next.js project. You may need to adjust the code to fit your existing project structure and coding conventions.

Here's an example of a component generated by Replay for a simple form:

typescript
// components/GeneratedForm.tsx
import { useState } from 'react';
import { supabase } from '../lib/supabaseClient';

const GeneratedForm = () => {
  const [email, setEmail] = useState('');
  const [password, setPassword] = useState('');
  const [loading, setLoading] = useState(false);
  const [error, setError] = useState<string | null>(null);

  const handleSubmit = async (e: React.FormEvent) => {
    e.preventDefault();
    setLoading(true);
    setError(null);

    try {
      const { data, error } = await supabase.auth.signUp({
        email: email,
        password: password,
      });

      if (error) {
        setError(error.message);
      } else {
        console.log('Sign up successful!', data);
        // Redirect or display success message
      }
    } catch (err: any) {
      setError(err.message);
    } finally {
      setLoading(false);
    }
  };

  return (
    <form onSubmit={handleSubmit}>
      {error && <p className="text-red-500">{error}</p>}
      <div>
        <label htmlFor="email">Email:</label>
        <input
          type="email"
          id="email"
          value={email}
          onChange={(e) => setEmail(e.target.value)}
          className="border rounded p-2"
        />
      </div>
      <div>
        <label htmlFor="password">Password:</label>
        <input
          type="password"
          id="password"
          value={password}
          onChange={(e) => setPassword(e.target.value)}
          className="border rounded p-2"
        />
      </div>
      <button type="submit" disabled={loading} className="bg-blue-500 text-white rounded p-2">
        {loading ? 'Loading...' : 'Sign Up'}
      </button>
    </form>
  );
};

export default GeneratedForm;

This component includes:

• •State management for form inputs (email and password)
• •Supabase integration for user signup
• •Error handling
• •Loading state

You can then import and use this component in your Next.js pages:

typescript
// pages/signup.tsx
import GeneratedForm from '../components/GeneratedForm';

const SignupPage = () => {
  return (
    <div>
      <h1>Sign Up</h1>
      <GeneratedForm />
    </div>
  );
};

export default SignupPage;

Step 5: Connect to MongoDB#

If your UI interacts with a database, you'll need to connect the generated code to your MongoDB database.

For example, if you have a component that displays a list of products, you can fetch the data from MongoDB using the

function we defined earlier.

typescript
// components/ProductList.tsx
import { useState, useEffect } from 'react';
import { connectToDatabase } from '../lib/mongodb';

interface Product {
  _id: string;
  name: string;
  price: number;
}

const ProductList = () => {
  const [products, setProducts] = useState<Product[]>([]);

  useEffect(() => {
    const fetchData = async () => {
      const { db } = await connectToDatabase();
      const productsData = await db.collection('products').find().toArray();
      setProducts(JSON.parse(JSON.stringify(productsData))); // Correctly serialize _id
    };

    fetchData();
  }, []);

  return (
    <ul>
      {products.map((product) => (
        <li key={product._id}>
          {product.name} - ${product.price}
        </li>
      ))}
    </ul>
  );
};

export default ProductList;

This component fetches a list of products from the

collection in your MongoDB database and displays them in a list. Note the to correctly serialize the field for use in React.

⚠️ Warning: Always sanitize user inputs to prevent SQL injection attacks.

Benefits of Using Replay with Next.js, MongoDB, and Supabase#

Using Replay in conjunction with Next.js, MongoDB, and Supabase offers several advantages:

• •Faster Development: Replay automates the process of generating UI code, allowing you to focus on more complex logic and features.
• •Improved Accuracy: Behavior-Driven Reconstruction ensures that the generated code accurately reflects the intended behavior of the UI.
• •Seamless Integration: Replay integrates seamlessly with Next.js, MongoDB, and Supabase, simplifying the process of building full-stack applications.
• •Reduced Errors: Automated code generation reduces the risk of human error, leading to more stable and reliable applications.
• •Enhanced Collaboration: Replay's Product Flow maps provide a visual representation of the application's structure, facilitating collaboration between developers and designers.

Frequently Asked Questions#

Is Replay free to use?#

Replay offers a free tier with limited features and usage. Paid plans are available for more advanced features and higher usage limits.

How is Replay different from v0.dev?#

v0.dev primarily uses text prompts to generate UI code. Replay, on the other hand, analyzes video recordings of user sessions, providing a more accurate and behavior-driven approach to UI reconstruction. Replay understands the intent behind the UI, not just its visual appearance.

What types of applications is Replay best suited for?#

Replay is particularly well-suited for rebuilding complex, multi-page UIs with intricate user flows. It is also beneficial for applications that require a high degree of accuracy and reliability.

What if the generated code isn't perfect?#

The code generated by Replay is a starting point. You will likely need to make adjustments and refinements to fit your specific needs. However, Replay significantly reduces the amount of manual coding required, saving you time and effort.

Does Replay support custom components?#

Yes, Replay allows you to integrate custom components into the generated code. This allows you to leverage your existing component library and maintain consistency across your application.

---

Ready to try behavior-driven code generation? Get started with Replay - transform any video into working code in seconds.