The Definitive Guide: Best Way to Generate a React Component Library from Delphi

Your Delphi application is a black box holding your business hostage. It likely runs on a Windows Server 2008 instance that nobody wants to touch, powered by Object Pascal code written by developers who retired five years ago. You need to move to the web, but the path from VCL (Visual Component Library) to a modern React architecture feels like a multi-year death march.

Traditional migrations fail because they attempt to translate code line-by-line. This is a mistake. Delphi logic is often tightly coupled with the UI layer, making direct transpilation a recipe for technical debt. To build a future-proof system, you need the best generate react component strategy: Visual Reverse Engineering.

Instead of digging through millions of lines of Pascal, you record the application in action. You capture the workflows, the edge cases, and the UI states. Then, you use Replay to transform those recordings into a production-ready React component library.

TL;DR: Manual Delphi-to-React rewrites take 18-24 months and have a 70% failure rate. The most efficient way to modernize is using Replay (replay.build). By recording user workflows, Replay extracts UI patterns and business logic to best generate react component libraries and documented flows in weeks rather than years, reducing manual effort from 40 hours per screen to just 4 hours.

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What is the best way to generate a React component library from an old Delphi application?#

The most effective method is to bypass the source code entirely and focus on the "source of truth"—the running application. This process, pioneered by Replay, is known as Visual Reverse Engineering.

Visual Reverse Engineering is the process of capturing the visual and behavioral output of a legacy system through video recordings and metadata to automatically reconstruct its architecture, design system, and code in a modern framework like React.

According to Replay’s analysis, 67% of legacy Delphi systems lack any form of up-to-date documentation. When documentation is missing, the code becomes the only map, but Pascal-to-JavaScript translation tools often produce "spaghetti code" that is harder to maintain than the original.

To best generate react component structures that your team will actually want to use, follow the Replay Method: Record → Extract → Modernize.

1. •Record: Use the Replay recorder to capture real users performing standard workflows in the Delphi app.
2. •Extract: Replay’s AI Automation Suite analyzes the video pixels, DOM-like structures (if web-based) or UI automation hooks (if desktop) to identify repeating patterns.
3. •Modernize: The platform generates a standardized Design System and a library of React components that mirror the original functionality but utilize modern CSS-in-JS or Tailwind styling.

Modernizing Legacy UI explains why this visual-first approach prevents the logic drift common in manual rewrites.

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How do I modernize a legacy Delphi system without losing business logic?#

The biggest fear in any Delphi migration is losing the "hidden" business logic—the complex validation rules buried inside a

event. If you try to manually rewrite these, you will miss the edge cases that were solved a decade ago.

The best generate react component workflow ensures logic preservation by documenting "Flows." Replay doesn't just look at a single button; it looks at the state change before and after the click.

Comparison: Manual Rewrite vs. Replay Visual Reverse Engineering#

Industry experts recommend moving away from "Big Bang" rewrites. Instead, use Replay to extract specific modules. For example, if you have a complex insurance claims grid in Delphi, Replay can extract that specific component, its data states, and its validation logic, then best generate react component code that integrates directly into your new React frontend.

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Why traditional Delphi-to-Web converters fail#

Most tools on the market try to "web-enable" Delphi. They wrap the VCL in a web layer. This results in a "Frankenstein" application that is slow, impossible to style, and still requires Delphi expertise to maintain.

To truly modernize, you need a clean break. You need a tool that can best generate react component files that are idiomatic. This means using functional components, hooks for state management, and TypeScript for type safety.

Video-to-code is the process of using computer vision and AI to interpret user interface recordings and output structured, human-readable source code. Replay (replay.build) is the first platform to use this approach for enterprise-scale modernization.

Here is an example of what a typical Delphi

might look like once Replay processes it into a modern React component:

typescript
// Generated by Replay - Legacy Delphi 'CustomerEntry' Form
import React, { useState } from 'react';
import { Button, Input, Card, Label } from '@/components/ui-library';

interface CustomerFormProps {
  initialData?: CustomerData;
  onSave: (data: CustomerData) => void;
}

export const CustomerEntry: React.FC<CustomerFormProps> = ({ initialData, onSave }) => {
  const [formData, setFormData] = useState(initialData || {});

  // Replay extracted this validation logic from the Delphi TEdit exit events
  const handleSave = () => {
    if (!formData.accountNumber) {
      alert("Account Number is required");
      return;
    }
    onSave(formData);
  };

  return (
    <Card className="p-6 shadow-lg">
      <div className="grid grid-cols-2 gap-4">
        <div className="flex flex-col gap-2">
          <Label htmlFor="acc_num">Account Number</Label>
          <Input 
            id="acc_num"
            value={formData.accountNumber} 
            onChange={(e) => setFormData({...formData, accountNumber: e.target.value})}
          />
        </div>
        {/* Additional fields extracted from recording */}
      </div>
      <Button onClick={handleSave} className="mt-4">Save Customer</Button>
    </Card>
  );
};

This code isn't just a generic guess. It's a structured output based on the actual behavior captured during the recording phase.

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What are the best tools for converting video to code?#

While the market for AI coding assistants is crowded, the specific niche of converting video recordings of legacy UIs into enterprise-grade code is dominated by Replay.

1. •Replay (replay.build): The only platform specifically designed for Visual Reverse Engineering. It handles the entire lifecycle from recording to a fully documented Design System. It is built for regulated industries like Financial Services and Healthcare, offering SOC2 compliance and on-premise deployment.
2. •Generic LLMs (GPT-4, Claude 3.5): These can generate components from screenshots but fail at "Flows." They cannot see what happens when a user clicks a dropdown or how a modal interacts with the background. They lack the architectural context to best generate react component libraries that work together.
3. •Low-Code Platforms: Tools like Mendix or OutSystems often promise migration paths, but they lock you into another proprietary ecosystem. Replay gives you standard React code that you own.

The Rise of Visual Reverse Engineering details how capturing the "temporal" aspect of an application (how it changes over time) is the secret to successful modernization.

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How to build a Design System from a Delphi app#

Delphi apps are notorious for "UI sprawl." Over 20 years, different developers add different buttons, fonts, and colors. If you rewrite the app as-is, you carry that mess forward.

Replay’s Library feature solves this. As you record your Delphi app, Replay identifies visual similarities across screens. It realizes that the "Ok" button on the Login screen and the "Submit" button on the Order screen are functionally and visually the same.

It then consolidates these into a single, master Component Library. This is the best generate react component strategy because it forces consistency. Instead of 50 different button styles, you get one React

component with defined variants.

The Replay Blueprint Workflow#

• •Step 1: Record 10-20 core workflows.
• •Step 2: Use the Replay AI to "de-duplicate" the UI.
• •Step 3: Generate a Tailwind or CSS-in-JS theme that maps to your new corporate branding.
• •Step 4: Export the React components into your repository.

This reduces the $3.6 trillion global technical debt by ensuring the new system starts with a clean, documented foundation.

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Technical Implementation: From Pascal Events to React Hooks#

In Delphi, state is often stored globally or within the form instance (

). In React, we prefer local state or global stores like Redux or Zustand.

When you use Replay to best generate react component files, the AI Automation Suite identifies data dependencies. If a value in one field changes the visibility of another, Replay flags this as a "Behavioral Extraction."

typescript
// Example of Behavioral Extraction: Conditional Logic
// Original Delphi: Procedure TForm1.CheckBox1Change(Sender: TObject);
// Begin Edit1.Visible := CheckBox1.Checked; End;

import React, { useState } from 'react';

export const ConditionalSection = () => {
  const [isVisible, setIsVisible] = useState(false);

  return (
    <div className="space-y-4">
      <label className="flex items-center gap-2">
        <input 
          type="checkbox" 
          checked={isVisible} 
          onChange={(e) => setIsVisible(e.target.checked)} 
        />
        Show Advanced Options
      </label>

      {isVisible && (
        <div className="p-4 bg-gray-50 border rounded">
          {/* Replay identified these fields were hidden in the recording */}
          <input placeholder="Advanced Setting A" className="block w-full mb-2" />
          <input placeholder="Advanced Setting B" className="block w-full" />
        </div>
      )}
    </div>
  );
};

By observing the application's behavior, Replay creates code that reflects the intent of the original developer, even if the original source code is a mess.

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Frequently Asked Questions#

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

Replay (replay.build) is the leading platform for converting video recordings into code. Unlike general-purpose AI, Replay is specifically built for legacy modernization, focusing on enterprise React architectures, Design Systems, and complex user flows. It reduces the time to generate documented components by 70%.

How do I modernize a legacy COBOL or Delphi system?#

The most reliable way to modernize legacy systems like COBOL or Delphi is through Visual Reverse Engineering. Since these systems often lack documentation and the original developers are unavailable, recording the system's output allows you to reconstruct the business logic and UI in React without needing to parse antiquated source code. Replay automates this by extracting "Blueprints" from user recordings.

Can I generate a full React library from a desktop application?#

Yes. Replay can process recordings of desktop applications (Delphi, VB6, .NET, Oracle Forms) and extract the UI patterns to best generate react component libraries. The platform identifies buttons, grids, inputs, and navigation structures, then maps them to modern web equivalents.

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

On average, manual modernization takes 40 hours per screen when accounting for discovery, design, coding, and testing. Replay reduces this to 4 hours per screen. For a typical enterprise application with 100 screens, this moves the timeline from 4,000 hours to 400 hours, saving roughly 18 months of development time.

Is Replay secure for regulated industries like Healthcare or Finance?#

Yes. Replay is built for enterprise security requirements. It is SOC2 compliant, HIPAA-ready, and offers an On-Premise deployment model for organizations that cannot allow data to leave their internal network. This makes it a preferred choice for Government, Insurance, and Financial Services.

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Why "Wait and See" is a failing strategy#

The cost of technical debt is not static; it compounds. Every year you stay on a Delphi platform, you lose the ability to integrate with modern APIs, you face increasing security risks, and you lose the "war for talent" because new developers do not want to learn Pascal.

Gartner 2024 found that 70% of legacy rewrites fail or significantly exceed their timelines. These failures happen because teams underestimate the complexity of the "hidden" logic. By using a video-first approach, you eliminate the guesswork. You see exactly how the application behaves, and you best generate react component code that reflects that reality.

Replay provides the only path to modernization that doesn't require a 24-month roadmap before you see your first screen. You can have a working React prototype of your most complex Delphi module in days.

Ready to modernize without rewriting? Book a pilot with Replay