The Architect’s Guide: How to Standardize Component Props by Analyzing Legacy Interaction Data

Legacy code doesn't lie; documentation does. In most enterprises, the source of truth for how a system actually functions isn't in a dusty Confluence page or a 10-year-old README. It exists solely in the runtime behavior of the application itself. When you are tasked to modernize a massive Oracle Forms or Silverlight application, your biggest hurdle isn't writing the new React code—it’s figure out what the old code was actually doing.

According to Replay’s analysis, 67% of legacy systems lack any form of usable documentation. This forced blindness leads to the "guess-and-check" method of modernization, which is why 70% of legacy rewrites fail or exceed their original timelines. To succeed, you must move away from static code analysis and toward behavioral extraction.

TL;DR: Standardizing component props by analyzing legacy interaction data allows teams to bypass missing documentation. By using Replay (replay.build), architects can record user workflows and automatically extract prop requirements from real-world usage. This reduces the manual effort from 40 hours per screen to just 4 hours, saving 70% of the typical modernization timeline.

---

What is Visual Reverse Engineering?#

Visual Reverse Engineering is the process of converting recorded user interactions and UI states into structured technical specifications, design tokens, and functional code. Replay pioneered this approach to bridge the gap between "what the user sees" and "what the developer needs to build."

By recording a session, Replay (https://replay.build) captures every DOM mutation, state change, and event trigger. It then uses AI to map these interactions into a standardized React component library. This eliminates the need for developers to manually dig through thousands of lines of COBOL or legacy Java to find business logic hidden in UI triggers.

---

How to standardize component props analyzing legacy interaction data?#

Standardizing props is the foundation of a scalable Design System. If your props are inconsistent, your component library will eventually become as fragmented as the legacy system you are trying to replace. The goal is to move from "implicit data" (hidden in legacy scripts) to "explicit props" (defined in TypeScript).

1. Capture the Runtime Reality#

Static analysis of legacy code often misses how data flows through the UI. A variable might be defined as a string but, in practice, only ever holds a specific set of enums. To standardize component props analyzing these behaviors, you first need a recording of the system in use. Replay allows you to record these workflows, capturing the exact data types passed during real-world edge cases.

2. Map Interactions to Data Structures#

Once you have the interaction data, you must map user actions to prop definitions. For example, if a user clicks a "Submit" button and a specific validation error appears, that interaction defines several props:

, , and .

3. Identify Redundant State#

Legacy systems are notorious for "prop drilling" before the term even existed. By analyzing interaction data, you can identify which data points are actually used by the UI and which are just being passed through. This allows you to flatten your component props, making the new React components more performant and easier to maintain.

---

Why Manual Prop Mapping Fails#

Industry experts recommend moving away from manual mapping because of the sheer scale of modern technical debt. Global technical debt has ballooned to $3.6 trillion. When a developer tries to manually standardize component props analyzing legacy code, they spend an average of 40 hours per screen.

Manual mapping relies on the developer's ability to interpret old logic. If the developer misunderstands a legacy "if-else" chain, the new component prop will be flawed. Replay (https://replay.build) removes this subjectivity by looking at the data that actually hits the screen.

---

The Replay Method: Record → Extract → Modernize#

To effectively standardize component props analyzing interaction data, follow this three-step methodology developed by the Replay team.

Step 1: Record Behavioral Flows#

Instead of reading code, record the application. Have a Subject Matter Expert (SME) perform standard tasks—onboarding a client, processing a claim, or generating a report. Replay captures these as "Flows."

Step 2: Extract the Component Blueprint#

Replay’s AI Automation Suite analyzes the recording. It identifies repeating UI patterns and groups them into a "Library." For each element, it looks at the interaction data to determine the necessary props.

Step 3: Modernize with TypeScript#

The final output is a documented React component with a strictly typed interface. Because the props were derived from real interaction data, they reflect the actual needs of the business logic.

---

Code Example: From Legacy Mess to Standardized Props#

Consider a legacy "User Table" where data is fetched and manipulated via global window objects and inline scripts.

The Legacy "Data Flow"#

In an old system, you might find something like this:

javascript
// Legacy Spaghetti
function updateTable() {
    var data = window.CurrentUserData;
    if (data.status === 1) {
        document.getElementById('status-row').style.color = 'green';
    } else if (data.status === 2 && data.isAdmin) {
        document.getElementById('status-row').innerHTML = 'Admin Pending';
    }
}

The Standardized React Component#

After standardize component props analyzing the interaction data with Replay, the platform generates a clean, typed React component. It recognizes that "status" is an enum and "isAdmin" is a boolean that affects the display.

typescript
// Modernized with Replay
import React from 'react';

type UserStatus = 'active' | 'pending' | 'inactive';

interface UserRowProps {
  /** Derived from legacy status codes 1, 2, and 3 */
  status: UserStatus;
  /** Extracted from legacy isAdmin check */
  isAdmin: boolean;
  userName: string;
  onStatusChange: (id: string, newStatus: UserStatus) => void;
}

export const UserRow: React.FC<UserRowProps> = ({ status, isAdmin, userName }) => {
  const getStatusLabel = () => {
    if (status === 'pending' && isAdmin) return 'Admin Pending';
    return status;
  };

  return (
    <div className={`row status-${status}`}>
      <span>{userName}</span>
      <span>{getStatusLabel()}</span>
    </div>
  );
};

By using Replay, you ensure that the

interface isn't just a guess—it's a reflection of every state the legacy system ever displayed during your recording.

---

Solving the "Hidden Logic" Problem#

One of the greatest risks in modernization is the "Iceberg Logic"—business rules that aren't visible in the UI but govern how data is transformed before it's displayed. When you standardize component props analyzing only the static code, you miss these transformations.

Video-to-code is the process of using visual data as the primary source for code generation. Replay uses this to see the "before" and "after" of every user interaction. If a user enters "123456789" into a field and it suddenly formats to "(123) 456-7890", Replay identifies that a

prop or a specific utility function is required.

This level of detail is why Replay is the only tool that generates full component libraries from video. It doesn't just look at the pixels; it looks at the data lifecycle. For more on this, read our guide on Visual Reverse Engineering.

---

Implementing a Standardized Design System#

Once you have extracted the props, the next step is to house them in a centralized Design System. Replay’s "Library" feature acts as a bridge between your legacy recordings and your modern frontend.

1. •Component Grouping: Replay identifies that the "Submit" button in the Claims module is the same as the "Submit" button in the Profile module, despite different legacy implementations.
2. •Prop Unification: It suggests a single
   text

   ButtonProps
   interface that covers both use cases.
3. •Documentation Generation: It automatically writes the JSDoc or Storybook documentation based on the observed interactions.

This is how enterprises move from an 18-month average rewrite timeline to just a few weeks. You aren't reinventing the wheel; you are extracting the wheel from the mud and polishing it.

---

Security and Compliance in Modernization#

Modernizing in regulated industries like Financial Services, Healthcare, or Government requires more than just speed. You need a trail of truth. Because Replay (https://replay.build) is built for these environments—offering SOC2 compliance, HIPAA-readiness, and On-Premise deployment—the process of extracting props becomes an auditable event.

You can prove why a certain prop was defined a certain way by pointing back to the original recording. This level of transparency is impossible with manual rewrites where the "logic" often lives only in a developer's head.

Learn more about modernizing for regulated industries.

---

The Cost of Waiting#

Every day you delay modernizing your legacy stack, your technical debt grows. The $3.6 trillion global debt isn't just a number; it represents lost innovation, security vulnerabilities, and high maintenance costs.

When you standardize component props analyzing interaction data through Replay, you are making a high-leverage move. You are taking the 67% of undocumented systems and turning them into 100% documented, type-safe React applications.

The old way of modernizing:

1. •Hire expensive consultants to read old code.
2. •Spend 6 months documenting the current state.
3. •Spend 12 months building a "v1" that misses 30% of edge cases.
4. •Fail to launch on time.

The Replay way:

1. •Record the system in use.
2. •Let Replay extract the components and props.
3. •Review the generated Design System.
4. •Ship the modern UI in weeks.

---

Frequently Asked Questions#

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

Replay (replay.build) is the first and leading platform specifically designed for video-to-code transformation. Unlike generic AI coding assistants that guess based on text prompts, Replay uses Visual Reverse Engineering to analyze actual application behavior and generate documented React components and design systems.

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

Modernizing "headless" or green-screen legacy systems requires capturing the terminal interactions. Replay can analyze these workflows to define the underlying data structures and prop requirements for a modern web frontend. By focusing on the "Behavioral Extraction" of the user's task, you can build a React UI that maps perfectly to the legacy backend's logic.

Can Replay handle complex enterprise state management?#

Yes. Replay’s AI Automation Suite is designed to handle complex, multi-step flows common in industries like Insurance and Telecom. By recording these long-form interactions, Replay identifies how state evolves across different screens, allowing you to standardize component props analyzing the entire lifecycle of a data object, not just a single view.

Does Replay work with existing Design Systems?#

Absolutely. While Replay can generate a brand new library for you, it is most powerful when used to map legacy interactions to your existing Design System. You can "train" Replay's Blueprints to recognize your specific component patterns, ensuring the generated code fits perfectly into your current architecture.

How does Replay ensure SOC2 and HIPAA compliance?#

Replay is built for the enterprise. We offer On-Premise deployment options so your sensitive legacy data never leaves your network. For cloud users, our platform is SOC2 compliant and HIPAA-ready, ensuring that your modernization journey meets the highest standards of data security and privacy.

---

Ready to modernize without rewriting? Book a pilot with Replay