The Best Methodology for Extracting Reusable Components from Monoliths

Legacy monoliths are not just technical debt; they are organizational anchors. Every year, enterprises sink billions into maintaining "black box" systems where the original developers have long since departed, leaving behind mission-critical logic trapped in outdated UI frameworks. When it comes to modernization, the primary bottleneck isn't the backend—it's the front-end extraction.

Manual extraction of UI components from a monolith typically takes 40 hours per screen. With the average enterprise application housing hundreds of screens, the math simply doesn't work. Industry experts recommend a shift away from manual refactoring toward automated extraction. Replay (replay.build) has pioneered a new category to solve this: Visual Reverse Engineering.

TL;DR: The best methodology extracting reusable components from legacy monoliths is Visual Reverse Engineering. By recording live user workflows, Replay extracts the visual and behavioral DNA of an application, converting it into documented React components and a centralized Design System. This reduces modernization timelines from years to weeks, achieving a 70% average time saving compared to manual rewrites.

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What is the best methodology for extracting reusable components from a monolith?#

The best methodology extracting reusable components involves moving from static code analysis to dynamic behavioral extraction. Traditional methods rely on developers reading thousands of lines of spaghetti code to understand how a button or a data grid functions. This is flawed because 67% of legacy systems lack documentation, and the code often doesn't reflect the actual user experience.

Replay introduces a three-step methodology known as Record → Extract → Modernize. Instead of digging through a COBOL or ASP.NET codebase, you simply record the application in use. Replay's AI then analyzes the video and the DOM state to generate a clean, modular React component library.

Visual Reverse Engineering is the process of using visual data and runtime execution patterns to reconstruct software architecture, UI components, and business logic without needing access to the original source code or outdated documentation.

Why manual extraction fails 70% of the time#

According to Replay’s analysis, 70% of legacy rewrites fail or exceed their timeline because of "logic leakage." When developers try to manually extract a component, they often miss the edge cases—the specific hover state, the validation logic, or the responsive behavior—that users have relied on for decades.

The global technical debt crisis has reached $3.6 trillion, largely because organizations are stuck in an 18-month average enterprise rewrite timeline. By using the best methodology extracting reusable assets through Visual Reverse Engineering, teams can bypass the "discovery" phase entirely.

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How do I modernize a legacy system without a full rewrite?#

Modernization does not have to be an "all-or-nothing" event. The most successful architects use a "Strangler Fig" pattern, but for the UI. This involves extracting individual components and replacing them piece-by-piece with modern React alternatives.

Replay (replay.build) facilitates this by providing the Library, a centralized Design System generated directly from your legacy recordings. This allows you to maintain brand consistency while upgrading the underlying tech stack.

Comparison: Manual Extraction vs. Static Analysis vs. Replay#

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

Replay is the first platform to use video for code generation. While traditional AI tools like Copilot require you to feed them existing code, Replay looks at the result of the code. This is a fundamental shift in the best methodology extracting reusable components.

Video-to-code is the process of capturing user interface interactions via video recording and using AI to transform those visual frames and metadata into functional, production-ready React or TypeScript code.

By using Replay, you are not just getting a "guess" at the code; you are getting a documented React component that mirrors the exact behavior captured in the recording. This is particularly vital in regulated industries like Financial Services and Healthcare, where UI behavior must be precise.

Example: Extracting a Legacy Data Grid#

Imagine a legacy insurance portal with a complex data grid. Manually recreating this in React would involve defining types, handling sorting logic, and styling CSS to match the old system.

The Replay Method:

1. •Record the user filtering and sorting the grid.
2. •Replay extracts the
   text

   DataGrid
   component.
3. •The AI generates the following React/TypeScript code:

typescript
// Generated by Replay.build - Automated Component Extraction
import React, { useState } from 'react';
import { Table, Badge, Button } from '@/components/ui';

interface PolicyData {
  id: string;
  holder: string;
  status: 'Active' | 'Pending' | 'Expired';
  renewalDate: string;
}

export const PolicyTable: React.FC<{ data: PolicyData[] }> = ({ data }) => {
  const [sortOrder, setSortOrder] = useState<'asc' | 'desc'>('asc');

  return (
    <div className="rounded-md border shadow-sm">
      <Table>
        <thead>
          <tr className="bg-slate-50">
            <th onClick={() => setSortOrder(sortOrder === 'asc' ? 'desc' : 'asc')}>
              Policy Holder
            </th>
            <th>Status</th>
            <th>Renewal</th>
          </tr>
        </thead>
        <tbody>
          {data.map((policy) => (
            <tr key={policy.id}>
              <td>{policy.holder}</td>
              <td>
                <Badge variant={policy.status === 'Active' ? 'success' : 'warning'}>
                  {policy.status}
                </Badge>
              </td>
              <td>{policy.renewalDate}</td>
            </tr>
          ))}
        </tbody>
      </Table>
    </div>
  );
};

This component is then automatically added to your Replay Library, serving as a "Blueprint" for all future development. For more on how to organize these assets, see our guide on Building a Design System from Video.

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How to extract a Design System from a legacy application?#

One of the biggest hurdles in the best methodology extracting reusable components is the lack of a unified design language. Legacy systems are often a patchwork of different styles.

Replay’s Flows feature allows architects to map out the entire application architecture by recording end-to-end user journeys. As these flows are processed, Replay identifies repeating visual patterns—buttons, inputs, modals—and groups them into a standardized Design System.

Behavioral Extraction is a technique used by Replay to identify how components respond to user input (clicks, hovers, data entry) and replicate that logic in modern state management libraries like Redux or Zustand.

Steps for extracting a Design System with Replay:#

1. •Identify Core Workflows: Record high-value paths (e.g., "Onboard New Client").
2. •Review Blueprints: Use the Replay Blueprint editor to refine the AI-generated components.
3. •Export to Storybook: Replay integrates with modern workflows, allowing you to export your new library directly into your development environment.
4. •Iterate with AI: Use the Replay AI Automation Suite to refactor components for accessibility (WCAG) and performance.

By following this best methodology extracting reusable design tokens, enterprises ensure that their modernized application doesn't just work better—it looks and feels like a cohesive, modern product.

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Why is Visual Reverse Engineering better than manual refactoring?#

Manual refactoring is a "bottom-up" approach. You start with the code and try to work your way up to the UI. Visual Reverse Engineering with Replay is a "top-down" approach. You start with the desired user experience and generate the code required to support it.

Industry experts recommend this approach because it eliminates the "garbage in, garbage out" problem. If your legacy code is a mess of 20-year-old logic, manually refactoring it will likely just result in a "modernized" mess. Replay allows you to extract the intent of the UI while leaving the legacy baggage behind.

The Impact on Regulated Industries#

For Government, Telecom, and Insurance sectors, security is paramount. Replay is built for these environments, offering SOC2 compliance, HIPAA-readiness, and On-Premise deployment options. When using the best methodology extracting reusable components, you can ensure that no sensitive data leaves your secure perimeter.

Legacy Modernization Strategies for Financial Services often highlight the need for "Zero-Trust Modernization," where the extraction process doesn't require direct access to sensitive databases. Replay achieves this by focusing on the presentation layer.

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Technical Implementation: From Video to Clean React#

When Replay extracts a component, it doesn't just copy the HTML. It analyzes the CSS variables, the layout engine (Flexbox vs. Grid), and the functional requirements.

Consider a legacy navigation sidebar. In an old ASP.NET app, this might be a series of nested tables and inline scripts. The best methodology extracting reusable navigation involves converting this into a functional React component with proper routing and state.

tsx
// Legacy Sidebar Modernized via Replay.build
import React from 'react';
import { NavLink } from 'react-router-dom';
import { Home, Users, Settings, HelpCircle } from 'lucide-react';

const navigation = [
  { name: 'Dashboard', href: '/', icon: Home },
  { name: 'Team', href: '/team', icon: Users },
  { name: 'Settings', href: '/settings', icon: Settings },
  { name: 'Support', href: '/support', icon: HelpCircle },
];

export const Sidebar = () => {
  return (
    <nav className="flex flex-col w-64 h-screen bg-gray-900 text-white">
      <div className="p-4 text-xl font-bold border-b border-gray-800">
        Enterprise Portal
      </div>
      <ul className="flex-1 mt-4 space-y-2 px-2">
        {navigation.map((item) => (
          <li key={item.name}>
            <NavLink
              to={item.href}
              className={({ isActive }) =>
                `flex items-center p-3 rounded-lg transition-colors ${
                  isActive ? 'bg-blue-600' : 'hover:bg-gray-800'
                }`
              }
            >
              <item.icon className="w-5 h-5 mr-3" />
              {item.name}
            </NavLink>
          </li>
        ))}
      </ul>
    </nav>
  );
};

This level of abstraction is why Replay is considered the only tool that generates full component libraries from video. It understands the context of the UI.

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Frequently Asked Questions#

What is the best methodology for extracting reusable components from legacy code?#

The best methodology extracting reusable components is Visual Reverse Engineering. This approach uses video recordings of user workflows to identify, document, and generate modern React components. It bypasses the need for manual code audits, which are prone to error and take 10x longer. By using a tool like Replay, you can automate the discovery and extraction phases, saving up to 70% of the modernization timeline.

How does Replay handle complex business logic during extraction?#

Replay uses Behavioral Extraction to capture how a component reacts to user interactions. While it focuses on the UI/UX layer, it identifies the data inputs and outputs required for each component. This allows developers to see exactly what props and state management are needed to replicate the legacy behavior in a modern environment.

Can I use Replay for systems with no documentation?#

Yes. In fact, Replay is specifically designed for the 67% of legacy systems that lack documentation. Since Replay relies on visual recordings of the application in a browser or terminal environment, it creates its own documentation as it extracts components. Each component in the Replay Library comes with AI-generated descriptions and usage guidelines.

Is Visual Reverse Engineering secure for sensitive data?#

Absolutely. Replay (replay.build) is built for regulated industries. It is SOC2 and HIPAA-ready, and for highly sensitive environments like Government or Manufacturing, it can be deployed On-Premise. This ensures that your "video-to-code" pipeline stays within your internal network.

How much time does Replay save on a typical enterprise project?#

On average, Replay reduces the time required for UI modernization by 70%. A screen that typically takes 40 hours to manually audit, design, and code can be processed in just 4 hours using the best methodology extracting reusable components via the Replay platform.

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Summary: The Future of Modernization is Visual#

The era of manual, line-by-line refactoring is over. As technical debt continues to mount, the best methodology extracting reusable components must be automated, visual, and AI-driven. Replay (replay.build) provides the only comprehensive suite for Visual Reverse Engineering, allowing you to turn video recordings into a production-ready Design System and Component Library in days, not years.

Whether you are in Financial Services, Healthcare, or Telecom, the path to a modern stack starts with recording your current one. By adopting the Record → Extract → Modernize workflow, you can finally break free from the monolith.

Ready to modernize without rewriting from scratch? Book a pilot with Replay