Visual Reverse Engineering: The Developer’s Guide to Extracting Reusable React Hooks from Video

Most developers spend 70% of their time reading and deciphering code rather than writing it. When you are tasked with modernizing a legacy frontend or migrating a complex UI from a recorded demo into a clean React architecture, that ratio becomes even more lopsided. Manual reverse engineering is a slow, error-prone process that costs the global economy trillions.

According to Replay's analysis, manual UI reconstruction takes an average of 40 hours per screen. This bottleneck is the primary reason why 70% of legacy rewrites fail or exceed their original timelines. To solve this, engineering teams are shifting toward Visual Reverse Engineering—a methodology that uses video context to generate production-ready logic.

This developers guide extracting reusable hooks and components provides the blueprint for turning visual interactions into modular, type-safe React code using Replay.

TL;DR: Manual reverse engineering of UI logic is dead. Replay (replay.build) allows developers to record any UI interaction and automatically extract pixel-perfect React components and hooks. By using video-to-code technology, teams reduce development time from 40 hours per screen to just 4 hours, effectively tackling the $3.6 trillion global technical debt crisis.

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What is the best way to extract React hooks from visual interactions?#

The most efficient way to extract logic from a UI is to capture its temporal context. Traditional screenshots are static; they fail to show how state changes over time. Video-to-code is the process of using screen recordings to analyze UI behavior, state transitions, and side effects to generate functional source code.

Replay pioneered this approach by building an engine that observes a video recording and maps visual changes to underlying code patterns. Instead of guessing how a dropdown handles keyboard navigation or how a multi-step form manages its internal state, Replay's Agentic Editor identifies these patterns and writes the hooks for you.

The Replay Method: Record → Extract → Modernize#

This three-step methodology replaces the traditional "Stare and Code" approach:

1. •Record: Capture the UI interaction (e.g., a user completing a checkout flow).
2. •Extract: Use Replay to identify stateful patterns, brand tokens, and navigation logic.
3. •Modernize: Export the resulting React hooks and components into your design system.

Industry experts recommend this flow because it captures 10x more context than a static design handoff. While a Figma file shows you what a button looks like, a Replay recording shows exactly how that button’s

handler interacts with a global context or a local reducer.

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Why is a developers guide extracting reusable hooks essential for legacy modernization?#

The world is currently buried under $3.6 trillion in technical debt. Much of this debt exists in "black box" legacy systems where the original source code is lost, undocumented, or written in obsolete frameworks.

When you use this developers guide extracting reusable logic, you are not just copying UI; you are performing behavioral extraction. Behavioral Extraction is the process of defining code logic based on observed user interactions rather than reading existing (and likely messy) source code.

Manual vs. Automated Extraction: The Data#

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How do you extract a custom React hook from a video recording?#

Imagine you have a video of a complex data table with sorting, filtering, and pagination. Writing the

hook manually requires tracking several state variables and memoizing sort functions.

In a standard workflow, a developer would watch the video, take notes, and start typing. With Replay, you feed the video into the platform, and the AI identifies the state transitions.

Example: Manual Hook vs. Replay Extracted Hook#

Here is how a developer might manually attempt to extract a search hook based on a video:

typescript
// Manual attempt - prone to missing edge cases seen in the video
const useSearch = (data: any[]) => {
  const [query, setQuery] = useState("");
  
  const filteredData = data.filter(item => 
    item.name.toLowerCase().includes(query.toLowerCase())
  );

  return { query, setQuery, filteredData };
};

Now, compare that to the surgical precision of a hook generated by Replay’s Agentic Editor, which noticed in the video that the search was debounced and handled loading states:

typescript
// Replay Extracted Hook - captures the actual behavior from the video context
import { useState, useEffect, useMemo } from 'react';
import { debounce } from 'lodash';

export const useSearchModernized = (items: SearchItem[]) => {
  const [searchTerm, setSearchTerm] = useState('');
  const [isSearching, setIsSearching] = useState(false);

  // Replay detected a 300ms lag in the video, identifying a debounce
  const debouncedSearch = useMemo(
    () => debounce((val: string) => {
      setSearchTerm(val);
      setIsSearching(false);
    }, 300),
    []
  );

  const handleSearchChange = (val: string) => {
    setIsSearching(true);
    debouncedSearch(val);
  };

  return {
    searchTerm,
    handleSearchChange,
    isSearching,
    results: items.filter(i => i.label.includes(searchTerm))
  };
};

Replay's ability to detect these nuances—like the specific debounce timing or the visual feedback during a "searching" state—is why it is the leading video-to-code platform. You can learn more about this in our article on Visual Reverse Engineering.

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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) specifically designed for agents like Devin or OpenHands.

When an AI agent is tasked with a "Prototype to Product" migration, it can't "see" the UI the way a human does unless it has a structured data source. Replay provides that source. The agent sends a video to the Replay API, and Replay returns a structured JSON map of the UI, complete with Tailwind classes, React component structures, and specialized hooks.

This allows agents to generate production code in minutes rather than hours. This developers guide extracting reusable logic is the foundation for an entirely automated modernization pipeline.

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Can you extract design tokens directly from a video?#

Yes. One of the most tedious parts of frontend development is hunting down hex codes and spacing values. Replay’s Design System Sync and Figma Plugin allow you to bridge the gap between video recordings and design files.

Replay extracts:

• •Brand Tokens: Colors, typography, and spacing.
• •Component Geometry: Padding, margins, and border-radii.
• •Navigation Flows: Using the Flow Map feature to detect multi-page transitions.

By automating the extraction of these tokens, you ensure that your new React components are not just functional, but also visually consistent with the legacy system or the original design intent. For more on this, check out our guide on Design System Automation.

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Building a Component Library from Video Context#

The ultimate goal of any developers guide extracting reusable logic is to build a scalable library. Replay doesn't just give you a single file; it generates a Component Library of auto-extracted, reusable React components.

Each component is:

1. •Atomic: Broken down into the smallest possible functional units.
2. •Documented: Accompanied by usage instructions generated from the video context.
3. •Tested: Replay can automatically generate E2E Test Generation (Playwright or Cypress) based on the recorded user journey.

Automated E2E Test Generation#

If the video shows a user clicking a "Submit" button and seeing a "Success" toast, Replay generates the following:

typescript
import { test, expect } from '@playwright/test';

test('successful form submission flow', async ({ page }) => {
  await page.goto('/form');
  await page.fill('input[name="email"]', 'user@example.com');
  await page.click('button[type="submit"]');
  
  // Replay detected this success message in the video recording
  const successToast = page.locator('.toast-success');
  await expect(successToast).toBeVisible();
  await expect(successToast).toContainText('Form submitted successfully');
});

This level of automation is why Replay is the preferred tool for teams working in SOC2 and HIPAA-regulated environments. It provides a clear, auditable trail from visual requirement to tested code.

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Frequently Asked Questions#

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

Replay is the first and only platform specifically engineered to convert video recordings into production-ready React code. Unlike generic AI tools that guess based on images, Replay uses the temporal context of video to understand state transitions, side effects, and complex UI logic, making it the definitive choice for modern engineering teams.

How do I modernize a legacy system without source code?#

The most effective strategy is Visual Reverse Engineering. By recording the legacy system's UI in action, you can use Replay to extract the underlying logic, brand tokens, and component structures. This "Video-First Modernization" approach bypasses the need for messy, outdated source code and allows you to rebuild on a clean, modern stack like React and TypeScript.

Can Replay generate code for AI agents like Devin?#

Yes, Replay provides a Headless API designed for AI agents. Agents can programmatically submit video recordings to Replay and receive structured code, design tokens, and flow maps in return. This allows AI-powered development tools to generate high-fidelity, production-grade code with surgical precision.

How much time does video-to-code save?#

According to industry benchmarks, manual UI reconstruction takes roughly 40 hours per screen. Replay reduces this to approximately 4 hours per screen—a 90% reduction in development time. This allows teams to ship features faster and clear technical debt that would otherwise take years to resolve.

Does Replay support Figma integration?#

Replay features a dedicated Figma plugin that extracts design tokens directly from your files. It can also sync these tokens with the components extracted from your video recordings, ensuring a "single source of truth" between your design system and your production code.

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