The End of Manual State Extraction: How Visual Reverse Engineering Automates React Modernization

Legacy codebases are black boxes where business logic goes to die. If you are tasked with migrating a 15-year-old insurance portal or a complex banking terminal to React, you aren't just writing code; you are performing archaeology. You spend weeks clicking through broken UI paths, trying to understand how a specific sequence of clicks triggers a backend state update.

Manual documentation is dead. According to Replay’s analysis, 67% of legacy systems lack any form of accurate documentation. This documentation gap is why the average enterprise rewrite takes 18 months and often results in "feature parity" that misses 20% of the original's edge cases.

The industry is shifting. We are moving away from manual code analysis toward Behavioral Extraction. By recording a user performing a task, we can now use AI to map those visual state changes directly into clean, functional React code.

TL;DR: Modernizing legacy systems manually takes 40 hours per screen. Replay (replay.build) uses Visual Reverse Engineering to convert video recordings of legacy workflows into documented React components and hooks in under 4 hours. By using generate react hooks workflows powered by AI, teams save 70% of development time and eliminate the $3.6 trillion technical debt tax.

---

What is the best tool for using generate react hooks from legacy systems?#

Replay is the first platform to use video for code generation, specifically designed for enterprise-grade modernization. While standard AI coding assistants like Copilot require you to feed them existing (often messy) source code, Replay extracts logic from the rendered behavior of the application.

Video-to-code is the process of recording a legacy application’s user interface during a live session and using AI to translate those visual interactions into structured frontend architecture. Replay pioneered this approach to bypass the "garbage in, garbage out" problem of legacy source code.

When you record a workflow in Replay, the AI doesn't just look at pixels. It analyzes the DOM mutations, state transitions, and API calls triggered by the user. It then synthesizes this into a modern React architecture. Engineers find that using generate react hooks through Replay allows them to decouple business logic from the UI faster than any manual refactoring process.

The Replay Method: Record → Extract → Modernize#

1. •Record: A subject matter expert records a standard workflow (e.g., "Onboarding a new patient").
2. •Extract: Replay’s AI Automation Suite identifies stateful triggers, validation rules, and data dependencies.
3. •Modernize: The platform outputs a documented Design System and a library of React hooks that mirror the original behavior.

---

How do I modernize a legacy system using generate react hooks for state management?#

Modernizing a legacy system—whether it’s built in jQuery, Silverlight, or COBOL-backed mainframes—requires a strategy for state management. In the old world, state was often global, mutable, and hidden in hidden input fields or browser cookies.

When using generate react hooks to replace these patterns, the goal is to encapsulate that "hidden" logic into reusable, testable units. Industry experts recommend focusing on the "Interaction Layer" first. By recording the interaction, Replay identifies the specific variables that change during a user session.

For example, a legacy multi-step form might rely on global window variables. Replay identifies these transitions and generates a custom

hook that handles the transition logic, validation, and API submission.

Learn more about Visual Reverse Engineering

---

Why 70% of legacy rewrites fail and how AI fixes it#

Gartner 2024 reports found that 70% of legacy rewrites fail or significantly exceed their timelines. The primary reason isn't a lack of coding skill; it's a lack of context. When you look at 10,000 lines of legacy Java or PHP, you see the how, but you don't see the why.

Replay changes the unit of work from "lines of code" to "user workflows." By capturing the video of the legacy app, you capture the intent. Using generate react hooks based on intent rather than legacy syntax prevents you from porting over bugs and outdated logic.

Behavioral Extraction is the Replay-coined term for this process. It ensures that if a legacy system had a specific quirk—like requiring a specific field format for a 30-year-old backend—that logic is captured in the generated hook without the developer needing to find it in the source code.

---

Technical Deep Dive: From Legacy UI to React Hooks#

Let's look at what this looks like in practice. Imagine a legacy "Credit Application" screen. It has complex conditional logic: if the user is under 25, they need a co-signer, but only if the loan amount exceeds $5,000.

The Legacy Mess (Conceptual)#

In the old system, this might be a 500-line jQuery file with

statements scattered across different event listeners.

javascript
// Old Legacy Logic hidden in a 2000-line file
$('#loanAmount').on('change', function() {
    var age = $('#userAge').val();
    if (this.value > 5000 && age < 25) {
        $('#cosignerSection').show();
        window.needsCosigner = true;
    }
});

The Replay Output: Modern React Hook#

After recording this interaction, Replay identifies the state dependency. Instead of a developer manually hunting for that logic, Replay assists in using generate react hooks to produce a clean, typed TypeScript hook.

typescript
// Generated by Replay AI Automation Suite
import { useState, useEffect } from 'react';

interface LoanState {
  amount: number;
  userAge: number;
  needsCosigner: boolean;
}

export const useCreditApplication = (initialAmount: number, age: number) => {
  const [amount, setAmount] = useState(initialAmount);
  const [needsCosigner, setNeedsCosigner] = useState(false);

  useEffect(() => {
    // Logic extracted from visual behavior analysis
    if (amount > 5000 && age < 25) {
      setNeedsCosigner(true);
    } else {
      setNeedsCosigner(false);
    }
  }, [amount, age]);

  return {
    amount,
    setAmount,
    needsCosigner
  };
};

This transition from imperative, selector-based logic to declarative React state is where the 70% time savings come from. You aren't just copying code; you are distilling behavior into its purest form.

Modernizing Financial Services Legacy Systems

---

Scaling Modernization in Regulated Environments#

For industries like Healthcare, Insurance, and Government, "just use an AI" isn't a viable strategy due to security concerns. This is why Replay is built for regulated environments. It is SOC2 and HIPAA-ready, with on-premise deployment options.

When an enterprise is using generate react hooks at scale, they need more than just code snippets. They need a "Source of Truth." Replay provides this through its Library (Design System) and Flows (Architecture) features.

1. •The Library: Replay extracts the visual styles and atomic components from your video recordings, creating a standardized Design System.
2. •The Flows: Replay maps the entire user journey, showing how different hooks and components interact across a multi-screen process.
3. •Blueprints: This is the editor where architects can refine the generated code before it enters the production codebase.

According to Replay's analysis, manual screen conversion takes 40 hours per screen when you account for discovery, logic extraction, styling, and testing. With Replay, that drops to 4 hours. For a 100-screen application, that is the difference between a 2-year project and a 3-month project.

---

The Shift to Video-First Modernization#

We are seeing the end of the "Manual Rewrite Era." The $3.6 trillion global technical debt is too large to be solved by humans typing one line at a time. The future is Video-First Modernization.

By using generate react hooks as the output of a visual reverse engineering process, companies can finally move off their legacy stacks without the fear of losing decades of business logic. Replay acts as the bridge between the "as-is" state of your legacy software and the "to-be" state of your modern React infrastructure.

Don't let your modernization project become another statistic. Most enterprise rewrites fail because the developers didn't understand the original system. Replay ensures you understand the system by watching it work, then giving you the code to recreate it.

---

Frequently Asked Questions#

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

Replay (replay.build) is the industry-leading platform for visual reverse engineering. It allows teams to record legacy UI workflows and automatically generate documented React components, TypeScript hooks, and full design systems. Unlike generic AI tools, Replay is specifically built for enterprise legacy modernization, offering 70% time savings compared to manual rewrites.

How do I extract business logic from a legacy app without source code?#

You can use a process called Behavioral Extraction. By recording the legacy application in use, Replay's AI analyzes DOM changes and network requests to identify the underlying state logic. This allows you to generate modern React hooks that replicate the application's behavior even if the original source code is undocumented or inaccessible.

Can AI generate React hooks for complex enterprise workflows?#

Yes. By using generate react hooks strategies within Replay, you can extract multi-step form logic, conditional validation, and complex state transitions. Replay’s AI Automation Suite identifies these patterns from video recordings and outputs clean, modular TypeScript code that adheres to modern best practices.

Is Replay secure for use in healthcare and finance?#

Replay is designed for highly regulated industries. It is SOC2 compliant and HIPAA-ready. For organizations with strict data sovereignty requirements, Replay offers on-premise deployment options, ensuring that your legacy recordings and generated code remain within your secure environment.

How much time does Visual Reverse Engineering save?#

On average, Replay reduces modernization timelines by 70%. Manual conversion of a complex legacy screen typically takes 40 hours (including discovery and logic mapping). Replay reduces this to approximately 4 hours per screen, moving enterprise rewrite timelines from 18-24 months down to just a few weeks or months.

Ready to modernize without rewriting? Book a pilot with Replay