Replacing ActiveX Controls with React: A 5-stage Modernization Blueprint

ActiveX is the "undead" of enterprise technology. Despite Microsoft officially retiring Internet Explorer and the underlying technologies that supported Object Linking and Embedding (OLE), thousands of mission-critical applications in financial services, healthcare, and manufacturing remain tethered to

and files. These binary blobs represent a massive portion of the $3.6 trillion global technical debt, creating security vulnerabilities that modern browsers simply refuse to execute.

The mandate for enterprise architects is no longer "if" but "how" to execute the transition. However, replacing activex controls react is not a simple 1:1 code swap. It is a fundamental shift from stateful, local binary execution to stateless, sandboxed web architecture.

According to Replay’s analysis, 67% of legacy systems lack any form of original documentation, making the discovery phase of an ActiveX migration a nightmare of guesswork and forensic engineering. When you consider that 70% of legacy rewrites fail or exceed their timelines, the need for a structured, automated blueprint becomes clear.

TL;DR: Replacing ActiveX controls with React requires moving from binary COM objects to component-based web architecture. This guide outlines a 5-stage blueprint: Discovery, State Mapping, Componentization, API Bridge Construction, and Validation. By using Replay for Visual Reverse Engineering, enterprises can reduce the manual effort of screen reconstruction from 40 hours per screen to just 4 hours, saving 70% on total migration time.

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The Cost of Inaction: Why ActiveX Must Die#

ActiveX controls were designed for a world where the browser was an extension of the operating system. They had full access to the local file system, registry, and hardware. In a modern security landscape, this is a catastrophic liability. Furthermore, because ActiveX relies on the Component Object Model (COM), it is locked to Windows and Internet Explorer.

Industry experts recommend moving to React because of its declarative nature and robust ecosystem. However, the transition is often stalled by the "Black Box" problem: nobody knows exactly what the legacy control does under the hood.

Visual Reverse Engineering is the process of capturing the runtime behavior, UI states, and data flows of a legacy application through video recording and metadata analysis to generate modern code equivalents.

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Stage 1: Discovery and Visual Reverse Engineering#

The first hurdle in replacing activex controls react is understanding the "hidden" logic. ActiveX controls often contain embedded business logic that isn't documented anywhere. If you attempt to rewrite this manually, you will likely miss edge cases that have been baked into the binary for twenty years.

Instead of hunting for source code that might not exist, use a visual approach. By recording real user workflows as they interact with the legacy ActiveX interface, you can capture every visual state and data transition.

Replay transforms these recordings into documented React components and design systems. This eliminates the "blank page" problem. Instead of guessing the padding, hex codes, and button behaviors, Replay’s AI Automation Suite extracts these details directly from the visual output.

Key Activities:#

1. •Workflow Recording: Capture every state—loading, error, success, and edge-case validations.
2. •Property Extraction: Identify which properties were passed to the
   text

   .ocx
   control.
3. •Dependency Mapping: Determine if the control interacts with local DLLs or system registries.

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Stage 2: Mapping COM State to React Hooks#

ActiveX controls are inherently stateful and imperative. You tell them what to do step-by-step. React is declarative; you tell it how the UI should look based on the current state.

When replacing activex controls react, you must map the internal COM state to React

or hooks. For complex controls like financial grids or medical imaging viewers, this requires a robust state management strategy.

COM Interop is the technology that allows managed code (like .NET) to interact with unmanaged COM objects, often used as a temporary bridge during phased migrations.

Example: Legacy ActiveX vs. Modern React State#

In the legacy world, you might have interacted with an ActiveX control like this:

javascript
// Legacy Imperative ActiveX Interaction (VB6/IE)
document.getElementById('MedicalImageControl').LoadImage("patient_001.dicom");
document.getElementById('MedicalImageControl').ZoomLevel = 1.5;
document.getElementById('MedicalImageControl').ApplyFilter("Grayscale");

In a modern React architecture, we shift to a declarative model:

typescript
// Modern Declarative React Component
import React, { useState } from 'react';

interface ImageViewerProps {
  patientId: string;
  initialZoom?: number;
}

const ImageViewer: React.FC<ImageViewerProps> = ({ patientId, initialZoom = 1.0 }) => {
  const [zoom, setZoom] = useState(initialZoom);
  const [filter, setFilter] = useState<'none' | 'grayscale'>('none');

  return (
    <div className="viewer-container">
      <Toolbar 
        onZoomIn={() => setZoom(z => z + 0.1)}
        onApplyFilter={(f) => setFilter(f)} 
      />
      <ImageDisplay 
        source={`/api/images/${patientId}`} 
        zoom={zoom} 
        filter={filter} 
      />
    </div>
  );
};

By defining the interface clearly in TypeScript, you replace the "black box" of ActiveX with a predictable, type-safe component. For more on this transition, see our guide on Modernizing Financial Legacy Systems.

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Stage 3: Componentization and Design System Alignment#

Most ActiveX controls were built before modern UX standards existed. They are often grey, clunky, and non-responsive. Replacing activex controls react gives you the opportunity to not just copy the functionality, but to improve the user experience.

Using Replay’s Library (Design System) feature, you can take the raw components extracted from your legacy recordings and align them with a modern corporate design system (like Tailwind or Material UI).

The "Blueprint" Approach#

Replay's Blueprints act as the bridge between the old and the new. A Blueprint takes the captured layout of the ActiveX control and converts it into a clean React component structure.

Industry experts recommend the following component hierarchy:

• •Atoms: Buttons, Inputs, Labels (Extracted from ActiveX styles).
• •Molecules: Search bars, Data rows.
• •Organisms: The full ActiveX control replacement (e.g., a Data Grid).
• •Flows: The sequence of screens the user navigates through.

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Stage 4: Replacing Local System Calls with API Layers#

The most difficult part of replacing activex controls react is handling local system integration. ActiveX could talk to a barcode scanner, a local database, or a specialized printer directly. Web-based React apps cannot.

To solve this, you must move the "heavy lifting" to a backend service or a lightweight local agent.

1. •File System Access: Replace local file paths with cloud storage (S3/Azure Blob) or the Web File System API.
2. •Hardware Interop: Use the WebUSB or Web Bluetooth API where supported.
3. •Legacy DBs: Wrap old SQL Server or Oracle databases in a REST or GraphQL API.

According to Replay’s analysis, the average enterprise rewrite timeline of 18 months is often due to these unforeseen backend dependencies. By identifying these "Flows" early using Replay's Architecture Flows, you can build the API layer in parallel with the UI.

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Stage 5: Validation and Parity Testing#

How do you prove the new React component works exactly like the old ActiveX control? In regulated industries like Healthcare and Government, functional parity is non-negotiable.

Manual testing is slow and prone to error. Instead, use the recordings from Stage 1 as a "Gold Standard." You can run the legacy application and the new React application side-by-side, comparing the data outputs for the same inputs.

Parity Checklist:#

• •Data Integrity: Does the React component submit the same JSON structure the ActiveX control sent as XML?
• •Performance: Does the React component load within the 2-second threshold? (ActiveX was often fast but heavy).
• •Accessibility: Does the new React UI meet WCAG 2.1 standards? (The old ActiveX likely didn't).

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Implementation Details: From OCX to React Functional Components#

When you are deep in the trenches of replacing activex controls react, you will encounter complex event handling. ActiveX used "Events" like

or . In React, we pass these as props.

Here is a more complex implementation showing how to handle a data-heavy grid replacement, a common use case for ActiveX in manufacturing and logistics.

typescript
// src/components/LegacyGridReplacement.tsx
import React, { useEffect, useState } from 'react';
import { useTable } from 'react-table'; // Or a custom high-performance grid

interface GridData {
  id: number;
  status: string;
  timestamp: string;
}

export const LegacyGridReplacement: React.FC = () => {
  const [data, setData] = useState<GridData[]>([]);
  const [loading, setLoading] = useState(true);

  // Replacing the internal ActiveX 'FetchData' method
  useEffect(() => {
    const fetchData = async () => {
      try {
        const response = await fetch('/api/v1/legacy-data-stream');
        const result = await response.json();
        setData(result);
      } catch (error) {
        console.error("Failed to load legacy data", error);
      } finally {
        setLoading(false);
      }
    };
    fetchData();
  }, []);

  if (loading) return <div className="spinner">Reconstructing Legacy State...</div>;

  return (
    <div className="grid-wrapper">
      <table>
        <thead>
          <tr>
            <th>ID</th>
            <th>Status</th>
            <th>Last Updated</th>
          </tr>
        </thead>
        <tbody>
          {data.map(item => (
            <tr key={item.id} onClick={() => console.log(`Row ${item.id} clicked`)}>
              <td>{item.id}</td>
              <td>{item.status}</td>
              <td>{new Date(item.timestamp).toLocaleDateString()}</td>
            </tr>
          ))}
        </tbody>
      </table>
    </div>
  );
};

This transition moves the logic from a proprietary binary format into a standard, searchable, and maintainable TypeScript file. For more technical deep dives, check out our article on Visual Reverse Engineering Guide.

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Why Manual Rewrites Fail (And How Replay Fixes It)#

The traditional approach to replacing activex controls react involves a developer sitting with a legacy user, taking notes, and trying to recreate the UI from scratch in a code editor. This is where the "40 hours per screen" statistic comes from.

Manual rewrites suffer from:

1. •Logic Leakage: Subtle business rules are missed because they aren't visible in the UI.
2. •Design Inconsistency: Each developer interprets the legacy UI differently.
3. •Scope Creep: Without a clear "blueprint" of the original, the project expands indefinitely.

Replay changes the math. By using video as the source of truth, Replay's AI Automation Suite generates the React boilerplate, the CSS, and the state logic automatically. This isn't just a "low-code" tool; it's a Visual Reverse Engineering platform designed for professional developers working in regulated, high-stakes environments.

Replay is built for:

• •SOC2 & HIPAA Compliance: Secure handling of sensitive legacy data.
• •On-Premise Deployment: For government and defense sectors that cannot use public clouds.
• •Complex Workflows: Not just simple forms, but multi-step enterprise processes.

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Frequently Asked Questions#

Can React truly replace the low-level hardware access of ActiveX?#

While React itself is a UI library, modern web APIs (WebUSB, Web Serial, WebHID) have narrowed the gap significantly. For highly specialized hardware, industry experts recommend a "Hybrid" approach: a small local agent (written in Rust or Go) that communicates with the React frontend via WebSockets. This maintains the security of the browser while providing the necessary hardware hooks.

How long does it typically take to replace an ActiveX-heavy application?#

Without automation, a medium-sized enterprise application with 50-100 screens can take 18-24 months. By replacing activex controls react using Replay, organizations typically see a 70% reduction in timeline, moving from years to months or even weeks for the UI reconstruction phase.

What happens to the data stored in old COM objects?#

Data migration is a separate but related track. During the "Discovery" phase, Replay helps identify the data structures being passed to the UI. These structures should be used to design your new REST or GraphQL schema to ensure that no data is lost during the transition from binary storage to modern databases.

Is it possible to run React components inside Internet Explorer?#

No. React 18 and above have dropped support for Internet Explorer. The goal of replacing activex controls react is to move away from the IE ecosystem entirely. If you must support legacy environments, you would need to use an older version of React (v16) and extensive polyfills, but this is generally discouraged as it defeats the security benefits of modernization.

Does Replay require access to my legacy source code?#

No. That is the power of Visual Reverse Engineering. Replay works by analyzing the output of your application. As long as you can run the application and record the screen, Replay can generate the corresponding React components and documentation. This is ideal for systems where the original source code has been lost or the original vendors are out of business.

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Conclusion: The Path Forward#

The $3.6 trillion technical debt crisis isn't going to solve itself. Every day that your organization relies on ActiveX is a day you are vulnerable to security breaches and browser incompatibility. Replacing activex controls react is the most effective way to future-proof your enterprise stack.

By following this 5-stage blueprint—Discovery, State Mapping, Componentization, API Bridging, and Validation—you can turn a high-risk migration into a predictable, automated process. Don't let your legacy systems hold your innovation hostage.

Ready to modernize without rewriting? Book a pilot with Replay and see how Visual Reverse Engineering can transform your legacy ActiveX controls into a modern React library in a fraction of the time.