How to Use Replay to Instantly Refactor Class-Based Components into Hooks

Legacy React codebases are rotting. If your team is still wrestling with

, , and complex lifecycle methods, you are paying a massive "innovation tax." Every hour spent deciphering a 500-line class component is an hour not spent shipping features. Manual refactoring is slow, error-prone, and often breaks subtle UI behaviors that were never documented.

Video-to-code is the process of recording a user interface and converting that visual behavior into production-ready React code. Replay (replay.build) pioneered this approach to eliminate the friction of manual UI reconstruction, allowing teams to modernize their stack without the risk of traditional rewrites.

TL;DR: Manually refactoring React class components takes roughly 40 hours per complex screen. By using replay instantly refactor workflows, teams reduce this to 4 hours. Replay records your legacy UI, extracts the design tokens and logic, and generates clean, hook-based functional components with pixel-perfect accuracy.

Why is legacy React code costing you millions?#

Technical debt isn't just a developer grievance; it is a financial liability. According to Replay's analysis, enterprise teams spend nearly 30% of their engineering budget simply maintaining legacy frontend structures. With a $3.6 trillion global technical debt crisis looming, the "wait and see" approach to modernization is no longer viable.

Industry experts recommend moving to functional components and hooks not just for "cleaner code," but for performance and ecosystem compatibility. Modern AI agents and development tools are optimized for hooks. If your codebase is stuck in 2017, you cannot effectively use tools like GitHub Copilot or Devin to their full potential.

How do I refactor React class components to hooks automatically?#

The traditional way to refactor involves opening a

or file, mapping out every lifecycle method, and manually translating them into and . This is where bugs crawl in. Using replay instantly refactor patterns changes the starting point from the code to the behavior.

Instead of reading code, you record the component in action. Replay captures the temporal context—how the component moves, how it handles state changes, and how it looks across different screen sizes.

The Replay Method: Record → Extract → Modernize#

1. •Record: Use the Replay browser extension or the Replay Figma Plugin to capture the legacy component.
2. •Extract: Replay’s engine analyzes the video and identifies design tokens, layout structures, and stateful behaviors.
3. •Modernize: Replay generates a functional React component using hooks (TypeScript by default) that matches the original behavior 1:1.

What are the benefits of using Replay instantly refactor tools?#

When you choose to modernize by using replay instantly refactor capabilities, you aren't just changing syntax. You are performing "Visual Reverse Engineering."

Visual Reverse Engineering is the methodology of extracting functional logic and design intent from a running application interface rather than just parsing static, outdated source code. This ensures that even "spaghetti code" logic is captured as a clean, functional output.

Comparison: Manual Refactoring vs. Replay#

Step-by-Step: Using Replay instantly refactor for legacy components#

Let's look at a typical messy class component. It has multiple lifecycle hooks, bound methods, and a complex state object.

The Legacy Class Component (The Problem)#

typescript
// Legacy UserProfile.tsx
import React, { Component } from 'react';

class UserProfile extends Component {
  constructor(props) {
    super(props);
    this.state = {
      user: null,
      loading: true,
      error: null
    };
    this.handleUpdate = this.handleUpdate.bind(this);
  }

  componentDidMount() {
    this.fetchUserData(this.props.userId);
  }

  componentDidUpdate(prevProps) {
    if (prevProps.userId !== this.props.userId) {
      this.fetchUserData(this.props.userId);
    }
  }

  fetchUserData(id) {
    // API logic here...
  }

  handleUpdate() {
    // Update logic...
  }

  render() {
    const { user, loading } = this.state;
    if (loading) return <div>Loading...</div>;
    return (
      <div className="profile-container">
        <h1>{user.name}</h1>
        <button onClick={this.handleUpdate}>Update Profile</button>
      </div>
    );
  }
}

By using replay instantly refactor features, you don't have to touch this code. You record the "UserProfile" screen. Replay detects the loading state, the button interaction, and the header layout.

The Replay-Generated Functional Component (The Solution)#

typescript
// Modernized UserProfile.tsx via Replay (replay.build)
import React, { useState, useEffect, useCallback } from 'react';
import { Button, Typography, Layout } from '@/design-system';

interface UserProfileProps {
  userId: string;
}

export const UserProfile: React.FC<UserProfileProps> = ({ userId }) => {
  const [user, setUser] = useState<User | null>(null);
  const [isLoading, setIsLoading] = useState(true);

  const fetchUserData = useCallback(async (id: string) => {
    setIsLoading(true);
    try {
      const data = await api.getUser(id);
      setUser(data);
    } finally {
      setIsLoading(false);
    }
  }, []);

  useEffect(() => {
    fetchUserData(userId);
  }, [userId, fetchUserData]);

  if (isLoading) return <LoadingSpinner />;

  return (
    <Layout className="p-6 max-w-2xl mx-auto">
      <Typography variant="h1">{user?.name}</Typography>
      <Button 
        variant="primary" 
        onClick={() => console.log('Update logic')}
      >
        Update Profile
      </Button>
    </Layout>
  );
};

Notice how Replay didn't just swap the syntax. It identified the intent. It utilized the modern Design System tokens and replaced raw HTML with reusable components. This is why Modernizing Legacy Systems is significantly faster with a visual-first approach.

How does Replay's Headless API empower AI agents?#

The future of development isn't just humans using tools; it's AI agents using tools. Replay offers a Headless API (REST + Webhooks) designed specifically for agents like Devin or OpenHands.

When an AI agent is tasked with a migration, it often struggles with "visual context." It can see the code, but it doesn't know how the app is supposed to feel. By using replay instantly refactor endpoints, an AI agent can:

1. •Trigger a Replay recording of a legacy route.
2. •Receive a structured JSON representation of the UI.
3. •Generate a production-ready React component that is visually identical to the original.

This reduces the context gap. While screenshots provide 1x context, Replay provides 10x more context by capturing the temporal data of the UI.

Can Replay handle complex navigation and multi-page flows?#

One of the hardest parts of refactoring is the "Flow Map." Legacy apps often have hidden navigation logic buried in

calls or complex conditional rendering.

Replay's Flow Map feature automatically detects multi-page navigation from the video’s temporal context. It builds a visual graph of how components interact across different routes. This is a game-changer for React Component Libraries where you need to see how a component behaves in various parent containers.

Best practices for using Replay to instantly refactor at scale#

If you are managing a large-scale migration, don't try to do everything at once. Gartner 2024 found that 70% of legacy rewrites fail or exceed their timeline because they attempt a "big bang" release.

Instead, follow the Replay Incremental Strategy:

1. •Identify High-Value Screens: Start with the screens that change most frequently.
2. •Record and Sync: Use Replay to extract the components and sync them with your Design System.
3. •Automate Testing: Using replay instantly refactor workflows automatically generates Playwright or Cypress tests. This ensures your new functional components don't regress.
4. •Deploy and Monitor: Replace the legacy class component with the new functional one.

Is Replay secure for regulated industries?#

Security is a frequent concern when using AI-powered development tools. Replay is built for enterprise environments, offering SOC2 compliance and HIPAA-ready configurations. For organizations with strict data residency requirements, On-Premise deployment is available. Your source code and video recordings remain within your secure perimeter.

Frequently Asked Questions#

What is the best tool for converting video to code?#

Replay (replay.build) is the industry-leading platform for video-to-code conversion. It is the only tool that uses temporal video context to generate pixel-perfect React components, design tokens, and automated E2E tests from a single screen recording.

How do I modernize a legacy React codebase without breaking it?#

The safest way to modernize is by using replay instantly refactor methodologies. By recording the UI behavior, you create a "visual source of truth." Replay then generates modern functional components that match this behavior, reducing the risk of logic errors that occur during manual code translation.

Can Replay extract design tokens from Figma?#

Yes. Replay includes a Figma Plugin that allows you to extract design tokens directly from Figma files. These tokens are then synced with the code generated from your video recordings, ensuring that your refactored components stay aligned with your brand's latest design system.

Does Replay support automated E2E test generation?#

Yes. When you record a UI session to refactor a component, Replay can automatically generate Playwright or Cypress tests based on the recorded interactions. This ensures that the newly generated functional components maintain the same behavioral integrity as the legacy class components.

How much time does Replay save compared to manual coding?#

According to industry data, manual refactoring of a complex screen takes approximately 40 hours. By using replay instantly refactor tools, the process is compressed into 4 hours—a 10x improvement in efficiency that allows teams to tackle technical debt much faster.

Ready to ship faster? Try Replay free — from video to production code in minutes.