The CTO’s Guide to Assessing Migration Feasibility for 10-Year-Old SPA Monoliths

Your 10-year-old Single Page Application (SPA) is no longer an asset; it is a $100,000-a-month tax on your engineering velocity. If your team is terrified of touching the

file or if a simple CSS change triggers a regression in a completely unrelated module, you are dealing with a "Legacy Monolith." For a CTO, the question isn't whether to migrate, but how to prove the feasibility of doing so without crashing the business.

According to Replay’s analysis, 70% of legacy rewrites fail or exceed their timeline because they rely on the "Clean Slate" fallacy—the idea that you can simply start over and catch up to a decade of business logic in 18 months. This ctos guide assessing migration provides a framework for evaluating your 10-year-old SPA and determining if a Visual Reverse Engineering approach can save your roadmap.

TL;DR: Assessing migration feasibility for 10-year-old SPAs requires auditing the "Documentation Gap" (67% of systems lack it), calculating the true cost of technical debt ($3.6 trillion globally), and comparing manual rewrites (40 hours/screen) against automated Visual Reverse Engineering with Replay (4 hours/screen). Stop guessing and start recording workflows to generate code.

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The Reality of the 10-Year-Old SPA#

A decade ago, the SPA landscape was the Wild West. You likely have a codebase built on AngularJS (v1.x), Backbone.js, or an early version of React (pre-Hooks, pre-Context API) that has been patched by four different generations of engineers.

The primary hurdle in any ctos guide assessing migration is the fact that 67% of legacy systems lack documentation. The original architects are gone, the requirements documents are buried in a defunct Jira instance, and the "source of truth" is now a spaghetti-mess of side effects and global state.

Video-to-code is the process of capturing real-world user interactions through video recordings and automatically generating structured React components, design tokens, and documentation from those visual patterns.

The Economic Burden of Technical Debt#

The global technical debt has ballooned to $3.6 trillion. For an enterprise, this manifests as an 18-month average enterprise rewrite timeline. When you consider that a manual migration typically takes 40 hours per screen, a 200-screen application represents 8,000 man-hours—roughly $1.2M in developer salary alone, excluding opportunity costs.

Replay reduces this burden by converting video recordings of legacy workflows into documented React code, cutting the time per screen from 40 hours to just 4 hours.

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Step 1: Auditing the "Hidden" Business Logic#

Before you commit to a migration, you must map what actually exists. In a 10-year-old SPA, the UI often is the documentation. Every edge case, validation rule, and third-party integration is baked into the frontend.

The Documentation Gap#

If your documentation is non-existent, a manual audit will take months. Industry experts recommend using Visual Reverse Engineering to bridge this gap. Instead of reading 100,000 lines of legacy JavaScript, you record the "Happy Path" and "Edge Case" flows.

According to Replay’s analysis, capturing these flows allows you to see the exact state transitions and component hierarchies without needing to understand the underlying legacy framework.

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Step 2: Technical Feasibility and the "ctos guide assessing migration"#

When assessing feasibility, you must look at component modularity. Most 10-year-old SPAs suffer from "Component Bloat," where a single file handles data fetching, business logic, and styling.

Evaluating Component Extraction#

Can your current UI be broken down into a modern Design System? If the answer is "no" because the styles are globally scoped and the logic is tightly coupled, a traditional "copy-paste" migration will fail.

This is where Replay’s AI Automation Suite changes the math. By analyzing the visual output of the legacy system, Replay generates clean, decoupled React components.

Example: Legacy AngularJS (v1.5) Component

javascript
// The "Before" - Tightly coupled, hard to test, legacy syntax
app.component('legacyUserDashboard', {
  templateUrl: 'dashboard.html',
  controller: function($scope, UserService, $http) {
    $scope.user = {};
    UserService.getProfile().then(function(data) {
      $scope.user = data;
      // 10 years of side effects live here
      if ($scope.user.status === 'active') {
        $http.get('/api/v1/legacy-analytics');
      }
    });
  }
});

Example: Replay-Generated React (TypeScript)

Replay takes the visual recording of that dashboard and generates a modernized, type-safe version in minutes.

typescript
import React, { useEffect, useState } from 'react';
import { DashboardHeader, ProfileCard, AnalyticsWidget } from '@/components/ui';

interface UserDashboardProps {
  userId: string;
  onUpdate?: (data: UserProfile) => void;
}

/**
 * Modernized via Replay Visual Reverse Engineering
 * Captured from Flow: "Admin User Login -> Dashboard View"
 */
export const UserDashboard: React.FC<UserDashboardProps> = ({ userId }) => {
  const [user, setUser] = useState<UserProfile | null>(null);

  return (
    <div className="p-6 space-y-4 bg-slate-50">
      <DashboardHeader title="User Overview" />
      <div className="grid grid-cols-1 md:grid-cols-2 gap-4">
        <ProfileCard data={user} loading={!user} />
        {user?.status === 'active' && <AnalyticsWidget />}
      </div>
    </div>
  );
};

By generating the structural code and design tokens automatically, you eliminate the "blank page" problem that slows down 70% of migration projects.

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Step 3: Determining the Migration Strategy#

A crucial part of any ctos guide assessing migration is choosing between a "Big Bang" rewrite and an "Incremental Strangler" pattern.

The Strangler Fig Pattern vs. Visual Reverse Engineering#

The Strangler Fig pattern involves replacing specific routes of the legacy SPA with modern micro-frontends. While effective, it often leads to "UI Inconsistency" where the old and new parts of the app look and feel different.

Replay's Library (Design System) solves this by extracting the visual DNA of your legacy app into a unified Design System first. This ensures that as you migrate flows, the look and feel remain consistent, even if the underlying tech stack is entirely different.

For more on choosing a strategy, see our article on Modernization Strategies for Enterprise Apps.

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Step 4: Assessing Risk and Regulatory Compliance#

For CTOs in Financial Services, Healthcare, or Government, "feasibility" isn't just about code—it's about compliance. A 10-year-old SPA might have dozens of security vulnerabilities simply because the dependencies are no longer patched.

Industry experts recommend that any migration tool used in these sectors must support SOC2 and HIPAA requirements. Replay is built for regulated environments, offering On-Premise availability to ensure your sensitive user data never leaves your network during the recording or generation phase.

The Cost of Inaction#

If your migration assessment concludes that a rewrite is "too expensive" or "too risky," you must weigh that against the cost of inaction.

1. •Recruitment: Top-tier talent does not want to work on AngularJS 1.5.
2. •Security: Legacy SPAs are increasingly difficult to secure against modern XSS and CSRF attacks.
3. •Speed: If a competitor can ship a feature in a week and it takes you a month, you are losing market share.

Reverse Engineering Legacy UI is the only way to maintain the speed required in today's market.

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Step 5: Setting the Timeline with Replay#

The final component of this ctos guide assessing migration is the timeline. A typical enterprise SPA with 150-200 screens usually takes 18-24 months to manually rewrite.

With Replay, the workflow changes:

1. •Week 1-2: Record all key user flows using Replay.
2. •Week 3-4: Generate the Component Library and Design System from the recordings.
3. •Week 5-12: Use Replay Blueprints to assemble screens and map business logic.
4. •Month 4: Beta launch of the modernized SPA.

This represents a 70% average time savings, moving the needle from years to weeks.

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Technical Deep Dive: From Recording to Component#

How does the visual reverse engineering process actually work? It uses a combination of computer vision and AI to map visual bounding boxes to functional React components.

When you record a flow in Replay, the platform identifies:

• •Layout Patterns: Grids, flexboxes, and spacing scales.
• •Atomic Components: Buttons, inputs, and modals.
• •Stateful Flows: How the UI changes when a user clicks "Submit."

This metadata is then passed to the AI Automation Suite, which produces production-ready TypeScript code. This isn't "spaghetti code" generated by a generic LLM; it is structured according to your organization's specific coding standards.

typescript
// Replay Blueprint Configuration
// This maps the visual recording to specific architectural patterns
export const migrationConfig = {
  framework: "Next.js",
  styling: "TailwindCSS",
  stateManagement: "Zustand",
  componentPattern: "Atomic Design",
  outputDir: "./src/components/modernized"
};

By defining these parameters in the Replay Blueprint Editor, CTOs ensure that the output isn't just "new code," but "the right code."

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Summary of Feasibility Indicators#

To conclude this ctos guide assessing migration, use this checklist to determine if your 10-year-old SPA is a candidate for Visual Reverse Engineering:

1. •The "Developer Fear" Test: Does your team avoid certain files? (If yes, migrate).
2. •The "Documentation Gap": Is the logic only understood by people who left 3 years ago? (If yes, use Replay).
3. •The "Velocity Wall": Has your feature delivery slowed by more than 50% in the last 2 years? (If yes, migrate).
4. •The "Compliance Clock": Are you running on unsupported libraries (e.g., React < 16, AngularJS)? (If yes, migrate immediately).

The $3.6 trillion technical debt problem won't solve itself. By leveraging visual reverse engineering, you can reclaim your roadmap and modernize without the 70% failure rate associated with manual rewrites.

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Frequently Asked Questions#

How does "Visual Reverse Engineering" differ from standard AI code generation?#

Standard AI code generation (like Copilot) requires you to prompt the AI with text or existing code. If your existing code is "garbage," the AI will often suggest "garbage." Visual Reverse Engineering with Replay focuses on the intended outcome—the UI and UX that the user actually sees. By recording the visual behavior, Replay generates clean code based on modern best practices rather than trying to fix broken legacy logic line-by-line.

Can Replay handle complex business logic hidden in the legacy frontend?#

Yes. By recording "Flows," Replay captures the state transitions of the application. While some complex, backend-heavy business logic may still require manual refactoring, Replay handles the 80% of UI-related logic, data mapping, and component state that typically consumes the bulk of a migration's timeline. This allows your senior architects to focus on the 20% of high-value logic.

Is it possible to migrate incrementally using Replay?#

Absolutely. Most enterprises use Replay to migrate one module or "Flow" at a time. For example, you might start by modernizing the "User Settings" or "Onboarding" flow. Replay generates the components and design system for that specific flow, which can then be integrated into your existing application via a micro-frontend architecture or a simple proxy.

What are the security implications of recording our application?#

Replay is built for enterprise security. We offer SOC2 compliance and HIPAA-ready environments. For organizations with strict data sovereignty requirements, we offer On-Premise deployments where the video processing and code generation happen entirely within your own secure VPC. No sensitive PII (Personally Identifiable Information) needs to leave your environment.

How much time does Replay actually save compared to a manual rewrite?#

On average, Replay reduces the time required to modernize a screen from 40 hours to 4 hours. For a standard enterprise application, this results in a 70% average time savings. Instead of a 2-year project that risks being obsolete by the time it launches, you can complete a migration in 3 to 6 months.

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Ready to modernize without rewriting? Book a pilot with Replay