Q90- How will you migrate Angular App to React App. What will be your approach?

Migrating from Angular to React requires careful planning, because both frameworks have different architectures, state management, and component lifecycle. A phased, step-by-step approach works best.

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1️⃣ Analyze the Current Angular App

• Identify modules, components, services, and routing
• Make a list of critical features to migrate first
• Note shared services, APIs, and third-party libraries

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2️⃣ Plan the Migration Strategy

Two common approaches:

A. Full Rewrite (Big Bang)

• Build the React app from scratch
• Only reuse APIs and assets from Angular
• Pros: Cleaner React architecture, modern best practices
• Cons: Time-consuming, high risk if the app is large

B. Incremental / Hybrid Migration

• Run Angular and React side by side
• Use a wrapper or micro-frontend architecture
• Migrate features one by one
• Pros: Less risk, users can continue using app
• Cons: Slightly more complex setup

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3️⃣ Setup React App

• Use Create React App (CRA), Vite, or Next.js
• Set up folder structure similar to Angular features for easier mapping
• Set up routing using react-router-dom

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4️⃣ Component Migration

• Convert Angular templates to JSX
• Convert Angular components & directives into React components
• Replace Angular pipes with React utility functions
• Replace ngIf/ngFor with JSX conditional rendering or .map()

// Angular
<li *ngFor="let item of items" *ngIf="item.visible">{{ item.name }}</li>

// React
{items.filter(item => item.visible).map(item => (
  <li key={item.id}>{item.name}</li>
))}

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5️⃣ Services / State Management

• Replace Angular services + dependency injection with React:
  • Context API for global state
  • Or Redux / Zustand / Recoil for complex state

// Angular service example
@Injectable({ providedIn: 'root' })
export class AuthService { ... }

// React context example
const AuthContext = React.createContext();

• Migrate HTTP calls from Angular HttpClient → React fetch / axios

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6️⃣ Routing & Navigation

• Angular RouterModule → React react-router-dom
• Migrate guards (canActivate) using ProtectedRoute components in React

<Route path="/dashboard" element={isLoggedIn ? <Dashboard /> : <Login />} />

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7️⃣ Third-Party Libraries

• Replace Angular-specific libraries (e.g., Angular Material) with React equivalents (e.g., Material UI, Ant Design)

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8️⃣ Testing

• Migrate unit tests from Karma/Jasmine → Jest + React Testing Library
• Ensure coverage for critical components and services

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9️⃣ Incremental Rollout (Optional)

• Use micro-frontends to render Angular and React together
• Gradually migrate feature by feature
• Once fully migrated → remove Angular entirely

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⚡ In short:

Migrating Angular to React is best done in phases: analyze the app → plan migration → set up React → migrate components, services, routing, and tests → optionally use hybrid deployment → finally remove Angular.