3. React

RRR:

A Lead React Developer is expected to combine strong React expertise, advanced JavaScript knowledge, architecture skills, and leadership abilities. Below is a structured skill set expected from a Lead React Developer.

1. Core JavaScript Expertise

A strong foundation in modern JavaScript is essential.

  • ES6+ features

    • Arrow functions

    • Destructuring

    • Spread/Rest operators

    • Modules (import/export)

  • Asynchronous programming

    • Promises

    • Async/Await

    • Fetch / Axios

  • Closures, Scope, Hoisting

  • Event loop and execution context

  • Functional programming concepts

2. Advanced React Skills

React Fundamentals

  • Components (Functional & Class)

  • Props and State

  • Lifecycle methods

  • React Hooks

    • useState

    • useEffect

    • useContext

    • useMemo

    • useCallback

    • Custom hooks

Advanced Concepts

  • React architecture design

  • Code splitting

  • Lazy loading

  • Error boundaries

  • Higher Order Components (HOC)

  • Render props

  • Context API

  • Performance optimization

3. State Management

Experience with scalable state management.

  • Redux / Redux Toolkit

  • Zustand / Recoil / MobX

  • Middleware

    • Redux Thunk

    • Redux Saga

  • Global state architecture

4. Type Safety

  • TypeScript

  • Generics

  • Interface design

  • Type-safe API calls

5. API Integration

  • REST APIs

  • GraphQL

  • API caching strategies

  • Error handling

  • Authentication

    • JWT

    • OAuth

6. Performance Optimization

  • React.memo

  • useMemo / useCallback

  • Virtualization

  • Bundle optimization

  • Lighthouse optimization

  • Avoid unnecessary re-renders

7. Testing

Testing is critical for lead-level roles.

  • Unit testing

  • Component testing

  • Integration testing

Tools:

  • Jest

  • React Testing Library

  • Cypress / Playwright

8. Build Tools & Ecosystem

Understanding frontend tooling.

  • Webpack

  • Vite

  • Babel

  • ESLint

  • Prettier

  • NPM / Yarn / PNPM

9. Frontend Architecture

Lead developers should design scalable systems.

  • Micro frontend architecture

  • Monorepo setups

  • Design patterns

  • Component libraries

  • Design systems

  • Module federation

10. UI & Styling

  • CSS3

  • Flexbox / Grid

  • Responsive design

  • Accessibility (a11y)

  • Styling tools:

    • Tailwind

    • Styled Components

    • SASS

    • Material UI / Ant Design

11. DevOps & Deployment

  • CI/CD pipelines

  • Docker basics

  • Cloud deployments

  • Static hosting

Platforms:

  • AWS

  • Vercel

  • Netlify

12. Leadership Skills

A Lead React Developer is also a technical leader.

  • Code reviews

  • Mentoring developers

  • Architecture decisions

  • Estimation and planning

  • Agile / Scrum participation

  • Stakeholder communication

13. Security Knowledge

  • XSS prevention

  • CSRF protection

  • Secure authentication

  • Secure API usage

14. Documentation & Collaboration

  • Writing technical documentation

  • Creating architecture diagrams

  • Maintaining coding standards

  • Working with product and UX teams

✅ Typical Lead React Developer Profile

  • 7–10+ years frontend experience

  • 4–6+ years React experience

  • Strong TypeScript knowledge

  • Architecture & leadership experience



https://www.linkedin.com/pulse/microfrontends-single-spa-migration-converting-app-rany/

https://lethanhan.medium.com/part-2-building-a-micro-frontend-app-with-single-spa-and-react-cra-549eb319c7a


React JD : 

  • JavaScript/TypeScript 
  • React: hooks, context, SSR/SSG awareness
  • Next.js or Vite-based React app
  • State Management: Redux Toolkit or Zustand + Async data: TanStack

Query/React Query

  • CSS Modules: Experience with modular CSS architecture and component[1]scoped styling
  • Styling: Tailwind and Material-UI component libraries
  • Authentication/Authorization: MSAL, OAuth2/OIDC, JWT and familiarity with

Azure Entra

  • API Integration: REST, Web Sockets, SSE; streaming UIs; backoff/retry;

cancellation

  • Testing: Jest, React Testing Library + E2E: Playwright or Cypress
  • Accessibility: WCAG 2.1 AA, keyboard nav, screen readers, color contrast
  • Performance: profiling, code-splitting, memoization, Core Web Vitals
  • Enterprise State Management: Complex state orchestration across multi-step

workflows and real-time updates

  • Security: OWASP Top 10, CSP, sanitization, dependency hygiene
  • Build/DevOps: GitHub Actions/Azure Pipelines, code splitting, environment

configs, Azure App Services

  • Observability: Application Insights and Matomo, logs/metrics/traces, client
error reporting

Awareness of cross-browser compatibility issues, 
inclusive interfaces aligned to WCAG/a11y best practices.
ensure SEO-friendly rendering (SSR/ISR).
component libraries (e.g., Storybook) for consistency and reuse.
Expertise in React, Next.js, TypeScript/JavaScript (ES6+), HTML5, and CSS3.
Participate in code reviews, troubleshooting, and debugging.
Knowledge of build tools like Webpack, Babel, NPM/Yarn.

 JD2:
(ReactJS, TypeScript, JavaScript, HTML, CSS, Redux, webpack, babel, Jest and related frameworks).

Measure and resolve performance bottlenecks, using tools like Chrome DevTools, Lighthouse, Webpage test, or custom tooling.
(webpagetest.org) , https://gtmetrix.com/ , https://tools.pingdom.com/, https://pagespeed.web.dev/

    Logging ; Monitoring tools like Quantum Metrics, Splunk, Grafana etc. 

JD3: 
Implement and optimize front-end logic using TypeScript with Zustand or similar state management libraries to ensure performance and persistence.
  • similar WebGL-based libraries.
  • Integrate and customize visualization frameworks like D3.js, Plotly.js, or Chart.js to create dynamic and insightful data views.
  • Architect and build React Microservices and modular components that ensure scalability and maintainability.
  • Flux / Redux / Zustand pattern

    • Cloud Workspace:
        Stackblitz
                    
        Github.com
            
            ReactGuide

            ReactAngularCombo

            ReactMFE

    Psychical workspace:

        E:/React_Workspace/
                3+ 5
        mfe
        reactguide



    Resources:

           YT- DipeshMalvia
                
            YT- Codevution        
            
            YT- TKS Sharm

            YT- Techsith

            YT- Coding The SmartWay

            github - sudheerj 

            YT- NetNinja

            YT- Code Nanban - Tamil



    Preparation:

    1. DipeshM- 1.1.react hooks - (9),  1.2.react for beginner- (30)


    React Interview Preparation Guide | React Learning Path 2022 | What & How to Learn for React upscale:
    https://www.youtube.com/watch?v=3HjP-IZ01bY

    Topics: 

    2. CEvalution- 

        2.1 React js tut -118
        2.2 React formik -44
        2.3 React Router -15
        2.4 React Styled Component - 10
        2.5 React Query -25
        2.6 React Redux - 30
        2.7 React Table -17
        2.8 React Story book -20
        2.9 React Typescript Webpack -8
        2.10 React with Typescript - 25
        2.11 React Practical - 14

     
    3. TKSSharma
            1. React Component Testing -18
            2. Testing React using Jest & Testing lib - 16
            3. React JS Interview Questions - 11
            4. React Hooks Crash course -(29)
            5. Build App in React - (35)
            6. React Formik - (25)
            7. React + Typescript - (16)
            8. React + Typescript + tailwind - (16)
            9. React + Redux - (12)
           10.HackerRank Interview -node, react, NG -(18)

    4. Techsith
            1. React Interview Questions (7)
            2. React Hooks Series (12)
            3. LeetCode (7)

     5. NNinja
            1. React Testing Library (14)
            2.  React Context and Hooks Tutorial (21)
            3. Full modern React Tutorial ( 32)
            4. React, Redux , firebase tutorial (40)

    simple form:

    Simple Form -2 











    export default function App() {



      const [state, setState] = useState({
        email: "",
        password: ""
      });

      const handleInputChange = (event) => {
        const { name, value } = event.target;
        setState((prevProps) => ({
          ...prevProps,
          [name]: value
        }));
      };

      const handleSubmit = (event) => {
        event.preventDefault();
        console.log(state);
      };

      return (
        <div className="App">
          <form onSubmit={handleSubmit}>
            <div className="form-control">
              <label>Email</label>
              <input
                type="text"
                name="email"
                value={state.email}
                onChange={handleInputChange}
              />
            </div>
            <div className="form-control">
              <label>Password</label>
              <input
                type="password"
                name="password"
                value={state.password}
                onChange={handleInputChange}
              />
            </div>
            <div className="form-control">
              <label></label>
              <button type="submit">Login</button>
            </div>
          </form>
        </div>
      );
    }

    simple form with error msg:

    import React, { useState } from "react";
    import ReactDOM from "react-dom";

    import "./styles.css";

    function App() {
      // React States
      const [errorMessages, setErrorMessages] = useState({});
      const [isSubmitted, setIsSubmitted] = useState(false);

      // User Login info
      const database = [
        {
          username: "user1",
          password: "pass1"
        },
        {
          username: "user2",
          password: "pass2"
        }
      ];

      const errors = {
        uname: "invalid username",
        pass: "invalid password"
      };

      const handleSubmit = (event) => {
        //Prevent page reload
        event.preventDefault();

        var { uname, pass } = document.forms[0];

        // Find user login info
        const userData = database.find((user) => user.username === uname.value);

        // Compare user info
        if (userData) {
          if (userData.password !== pass.value) {
            // Invalid password
            setErrorMessages({ name: "pass", message: errors.pass });
          } else {
            setIsSubmitted(true);
          }
        } else {
          // Username not found
          setErrorMessages({ name: "uname", message: errors.uname });
        }
      };

      // Generate JSX code for error message
      const renderErrorMessage = (name) =>
        name === errorMessages.name && (
          <div className="error">{errorMessages.message}</div>
        );

      // JSX code for login form
      const renderForm = (
        <div className="form">
          <form onSubmit={handleSubmit}>
            <div className="input-container">
              <label>Username </label>
              <input type="text" name="uname" required />
              {renderErrorMessage("uname")}
            </div>
            <div className="input-container">
              <label>Password </label>
              <input type="password" name="pass" required />
              {renderErrorMessage("pass")}
            </div>
            <div className="button-container">
              <input type="submit" />
            </div>
          </form>
        </div>
      );

      return (
        <div className="app">
          <div className="login-form">
            <div className="title">Sign In</div>
            {isSubmitted ? <div>User is successfully logged in</div> : renderForm}
          </div>
        </div>
      );
    }

    export default App;

    REact Hooks form :
    // inside src/App.js
    // Replace previous code with this.

    import React from "react";
    import { useForm } from "react-hook-form";
    import "./App.css";

    function App() {
    const { register, handleSubmit, formState: { errors } } = useForm();

    //const onSubmit = (data) => console.log(data);
    const onSubmit = (data) => {
        localStorage.setItem(data.email, JSON.stringify({ 
            name: data.name, password: data.password 
        }));
        console.log(JSON.parse(localStorage.getItem(data.email)));
      };

    return (
    <>
    <p className="title">Registration Form</p>

    <form className="App" onSubmit={handleSubmit(onSubmit)}>
    <input type="text" {...register("name")} />
    <input type="email" {...register("email", { required: true })} />
    {errors.email && <span style={{ color: "red" }}>
    *Email* is mandatory </span>}
    <input type="password" {...register("password")} />
    <input type={"submit"} style={{ backgroundColor: "#a1eafb" }} />
    </form>
    </>
    );
    }
    export default App;


    // inside src/Login.jsx

    import React from "react";
    import { useForm } from "react-hook-form";
    import "./App.css";

    function Login() {
    const {
    register,
    handleSubmit,
    formState: { errors },
    } = useForm();

    const onSubmit = (data) => {
    const userData = JSON.parse(localStorage.getItem(data.email));
    if (userData) { // getItem can return actual value or null
    if (userData.password === data.password) {
    console.log(userData.name + " You Are Successfully Logged In");
    } else {
    console.log("Email or Password is not matching with our record");
    }
    } else {
    console.log("Email or Password is not matching with our record");
    }
    };
    return (
    <>
    <p className="title">Login Form</p>

    <form className="App" onSubmit={handleSubmit(onSubmit)}>
    <input type="email" {...register("email", { required: true })} />
    {errors.email && <span style={{ color: "red" }}>
    *Email* is mandatory </span>}
    <input type="password" {...register("password")} />
    <input type={"submit"} style={{ backgroundColor: "#a1eafb" }} />
    </form>
    </>
    );
    }
    export default Login;


               

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