IndianTechnoEra: React Developer's Comprehensive Quiz: FaQ

Welcome to our comprehensive guide to React.js! Whether you're a seasoned React developer or just starting with this powerful JavaScript library, this collection of the top 30 questions and answers will help you enhance your understanding of React.js. Let's dive into the world of React and explore various aspects of this technology.

🚀 Embrace the Power of React 🚀

Welcome, fellow React enthusiasts and aspiring developers! Whether you're diving into React for the first time or looking to enhance your skills, you've landed in the right place. Our ReactJS Knowledge Hub is here to be your go-to resource for everything React-related.

🔍 Explore React Fundamentals: Delve into the core concepts, understand how components work, and master the art of state management. From JSX syntax to React Hooks, we've got you covered.

🌐 React in the Real World: Discover practical tips and best practices for building scalable, efficient, and maintainable React applications. Stay updated with the latest trends and industry insights.

🔗 Routing with React Router: Navigate the complexities of single-page applications effortlessly using React Router. Learn how to structure your app for seamless user experiences.

🔧 Redux Demystified: Unravel the mysteries of state management with Redux. Dive deep into actions, reducers, and the Redux store to architect robust applications.

💡 Problem-Solving with React: Tackle common challenges and find solutions to optimize your React code. From performance optimization to responsive design, enhance your problem-solving skills.

🤝 Community Collaboration: Connect with other React enthusiasts, share your experiences, and seek advice from the vibrant React community. Together, let's grow and excel in the world of React development.

🛠️ Hands-On Coding Challenges: Sharpen your skills with hands-on coding challenges. Apply your knowledge, experiment with different approaches, and elevate your coding proficiency.

📚 30 React Questions Series: Take a deep dive into our 30 React Questions Series. Test your knowledge, learn new concepts, and solidify your understanding with detailed answers.

🌟 Your React Journey Starts Here: Whether you're a seasoned developer or just starting, our goal is to empower you on your React journey. Let's code, learn, and innovate together!

Ready to embark on a React adventure? Let's dive in and make React development an exciting and rewarding experience. Happy coding!

🚀 Let's React and Roll! 🚀

Q1 of 30:

Question: Observe the below given JavaScript code and predict the JSX equivalent syntax from the given options.

const App = () => {

  return React.createElement("div", null, React.createElement("h1", {}, "Hello World"), React.createElement("p", null));

}

export default App;

Options:

1. <div> <h1> Hello World </h1> <p>null</p> </div>
2. <div> <h1> Hello World </h1> <p> </p> </div>
3. <div>null <h1> Hello World </h1> <p> null</p> </div>
4. <div null> <h1> Hello World </h1> <p null> </p> </div>

Answer:

2. <div> <h1> Hello World </h1> <p> </p> </div>

Q2 of 30: 

Question: Sophie is using React Router in her SPA and wants to create a link that can help her to navigate to "/products" URL. Select the appropriate line of code from the below options.

Options:

1. <Link href="/products">Products</Link>
2. <a href="/products">Products</a>
3. <Link to="/products">Products</Link>
4. <Link path="/products">Products</Link>

Answer:

3. <Link to="/products">Products</Link>

Q3 of 30:

Question: Match the following React methods (Set A) to its category (Set B).

Set A:

a. ReactDOM.unmountComponentAtNode();

b. useState

c. render()

d. defaultProps

Set B:

a. Handling props

b. Return JSX elements

c. Data handling

d. React DOM method

Options:

• a - c, b - a, c - d, d - b
• a - c, b - b, c - d, d - a
• a - d, b - c, c - b, d - a
• a - a, b - b, c - d, d - c

Answer:

2. a - c, b - b, c - d, d - a

Q4 of 30:

Question: Consider the below given code snippet. Choose the correct output from below options when it is rendered:

function Warning(props){

  if(!props.warn){

    return <div>No Warning..!!</div>;

  }

  return(

    <div>Warning..!!</div>

  )

}

function DisplayWarning(){

  const [status,setStatus] = useState(true)

  return(

    <Warning warn={status}/>

  )

}

ReactDOM.render(<DisplayWarning />, document.getElementById('root'))

Options:

1. Component rendered without any output
2. No Warning..!!
3. Warning..!!
4. Error: Warning Component not found

Answer:

3. Warning..!!

Q5 of 30:

Question: Consider the below code snippet:

const mapStateToProps = (state) => {

  return {

    courses: state.courses

  }

};

const mapDispatchToProps = (dispatch) => {

  return {

    createCourse: course => dispatch(courseActions.createCourse(course))

  }

};

const CourseDetails = () => {

  return (

    // JSX elements

  )

}

Identify the correct option to connect the React component to Redux stores:

Options:

1. connect(mapStateToProps, mapDispatchToProps)(CourseDetails);
2. connect(mapStateToProps(), mapDispatchToProps())(CourseDetails);
3. connect(mapStateToProps(state), mapDispatchToProps(dispatch))(CourseDetails);
4. connect(mapStateToProps), (mapDispatchToProps)(CourseDetails);

Answer:

1. connect(mapStateToProps, mapDispatchToProps)(CourseDetails);

Q6 of 30:

Question: Which of the following statement is/are false about React JS?

a. React JS uses phantom js to render the webpages on server-side

b. React JS is a framework

c. React JS improves the performance of the applications by using the concept of virtual DOM

d. In React JS, the data flow will happen in a single direction

Options:

1. a, b and d
2. Both b and d
3. Both a and b
4. Only b

Answer:

1. a, b and d

Q7 of 30:

Question: Order the below steps to match the data flow in Redux

a. The root reducer combines the new state returned from multiple reducers into a single state

b. Component dispatches an action

c. The store gets the initial state from root reducer passed to it

d. The action reaches the root reducer

e. Store saves the entire state of the application

Options:

1. c, b, d, a, e
2. c, b, a, d, e
3. a, c, b, d, e
4. a, c, d, b, e

Answer:

2. c, b, a, d, e

Q8 of 30:

Question: John is developing a functionality, where on clicking view details button of a particular product from the list of products, the details of that product should be displayed in a different view. For that, he is passing the productId through the URL. Choose the appropriate code snippet to achieve the requirement

Options:

1. let params = useParams(); {params.productId}
2. {useParams().productId}
3. both a and b
4. neither a nor b

Answer:

3. both a and b

Q9 of 30:

Question: Predict the output of the below given code snippet when it is rendered:

const Calculator = () => {

  var a = 7;

  var b = 6;

  var c = 5;

  return <h1>{"(a+b)-c"}</h1>;

};

Options:

1. a+b-c
2. 8
3. (a+b)-c
4. 7

Answer:

3. (a+b)-c

Q10 of 30:

Question: Consider the given two components Home and Contact.

The requirement is to render the Contact component within Home when the Home component is rendered

const Home = () => {

  return (

    <div>

      <p>Below, you can find the contact of the R&D Department.</p>

      <Contact />

    </div>

  );

};

const Contact = () => {

  return (

    <div>

      <p>123 Southern Avenue, Brooksville, Ph: 9999987878</p>

    </div>

  );

};

export default Home;

Select the appropriate way to achieve the requirement

Options:

1. ReactDOM.render(<Home></Home>, document.getElementById('root'))
2. ReactDOM.render(<Contact> , document.getElementById('root'))
3. ReactDOM.render(<Home />, document.getElementById('root'))
4. ReactDOM.render({Contact}, document.getElementById('root'))

Answer:

3. ReactDOM.render(<Home />, document.getElementById('root'))

Q11 of 30:

Question: The counter is passed with the initial value 0 to the reducer and the counter will be incremented by 1 when the increment button is clicked. When clicked on the increment button CallIncrement() function is called.

The action file is as shown below:

/* action file */

function onIncrement(step){

  return {

    type:"INC",

    step

  }

}

export function CallIncrement(){

  return (dispatch,getState)=>{

    setTimeout(()=>{

      console.log(getState())

      dispatch(onIncrement());

    },3000)

  }

}

What value would be logged to the console when the increment button is clicked for the third time?

Options:

1. Error because getState() method can be called only using the store object
2. 3
3. 2
4. Error because getState() method cannot be called within middleware function

Answer:

3. 2

Q12 of 30:

Question: Which of the below methods helps in unmounting a component from the DOM

Options:

1. unmountComponentAtNode
2. unmountComponent
3. useEffect
4. componentWillUnmount

Answer:

1. unmountComponentAtNode

Q13 of 30:

Question: Jemmy, a React developer, has a requirement of handling state in a functional component and she has written the below code:

const App = () => {

  const [count, setCount] = useState(0);

}

Which of the below statements should she use to increment the count variable of the above component?

Options:

1. setCount(count + 1);
2. this.setState({ this.state.count + 1 });
3. this.setCount(count + 1);
4. setCount(this.count + 1);

Answer:

1. setCount(count + 1);

Q14 of 30:

Question: Given below are the different ways a JSX expressions might be used to evaluate a certain condition. Choose the option(s) with no error:

a. )

return <div> {name === "Jade" ? "Hello, Jade!" : "No name found"} </div>;

b. )

if (name === "Jade") {

  var message = "Hello, Jade!";

} else {

  message = "No name found";

}

return <div>{message}</div>;

Options:

1. Option a
2. Option b
3. Both a and b
4. None of the options

Answer:

3. Both a and b

Q15 of 30:

Question: Which of the following h1 element will be rendered with styles?

<h1 style={{color: "Blue"; font-family:"Arial"}}> I'm styled </h1>

<h1 style={{color: "Blue font-family:Arial"}}> I'm styled </h1>

<h1 style={{color: "Blue",fontFamily:"Arial"}}> I'm styled </h1>

<h1 style={{color: "Blue",FontFamily:"Arial"}}> I'm styled </h1>

Options:

1. The first h1 element
2. The second h1 element
3. The third h1 element
4. The fourth h1 element

Answer:

3. The third h1 element

Q16 of 30:

Question: Listed below are the two components Home and Product. When you click the "Buy Now" button in the Product, that component should be added to the cart. Select the appropriate code from the options given to be written inside the handleClick() method in the Product component so that productId will be passed to the Home component. All the required import and export statements are included.

function Home() {

  const handleAdd = (productId) => {

    //Implement logic to purchase the specified product.

  };

  return <Product onPurchase={handleAdd} />;

}

export default Home;

function Product(props) {

  const [productId, setProductId] = useState("p-023");

  const handleClick = () => {

    //Select the appropriate line of code.

  };

  return (

    <div>

      <div>MobilePhone</div>

      <div>Price:1234</div>

      <button onClick={handleClick}>Buy Now</button>

    </div>

  );

}

Options:

1. Home.handleAdd(productId);
2. props.onPurchase(productId);
3. handleAdd(productId);
4. useNavigate(productId)

Answer:

2. props.onPurchase(productId);

Q17 of 30:

Question: The below code snippet produces a compilation error. Identify the options that help in removing the compilation error (Assume all the required environment setup has been done with the HTML file ready):

const Button = () => {

  const [cntr, setCntr] = useState(100);

  return (

    <div>

      <button onClick={handleClick}>update</button>

      <Resultant new={cntr} />

    </div>

  );

};

const Resultant = (props) => {

  const handleClick = () => {

    setCntr(cntr + 1);

  };

  return (

    <div>

      <h2>{props.new}</h2>

    </div>

  );

};

export default Button;

ReactDOM.render(<Button />, document.getElementById("root"));

Options:

1. Passing handleClick method from Resultant to Button component
2. Defining the handleClick method within the Button component
3. Binding the handleClick method in Resultant component
4. Defining the cntr state within Resultant component

Answer:

2. Defining the handleClick method within the Button component

Q18 of 30:

Question: Which of the following is the correct way to update the state?

a.

const auth = function(state = {status: 'logged out', value: 'guest'}, action) { 

  switch (action.type) { 

    case 'LOGIN': 

      return Object.assign({}, state, { 

        status: 'logged in', 

        value: action.value 

      }) 

  }

}

b.

const auth = function(state = {status: 'logged out', value: 'guest'}, action) { 

  switch (action.type) { 

    case 'LOGIN': 

      let newState=Object.assign({}, state, { 

        status: 'logged in', 

        value: action.value 

      })

      return newState; 

  }

}

c. 

const auth = function(state = {status: 'logged out', value: 'guest'}, action) { 

  switch (action.type) { 

    case 'LOGIN': 

      let newState= { 

        status: 'logged in', 

        value: action.value 

      }

      return newState; 

  }

}

d.

const auth = function(state = {status: 'logged out', value: 'guest'}, action) { 

  switch (action.type) { 

    case 'LOGIN': 

      state={      

        status: 'logged in', 

        value: action.value 

      }

      return state; 

  }

}

Options:

1. Both a and b
2. Only a
3. Both c and d
4. All of the given options

Answer:

1. Both a and b

Q19 of 30:

Question: Consider the below Reducers.

const Reducer1 = (state={

    currentDepts:{

        a1:"a101",b1:"a102",c1:"a103",d1:"a104"

    }

},action) =>{           

          return Object.assign({},state,{ currentDepts:{a1:"a201",b1:"a202",c1:"a203",d1:"a204"}});

}

export default Reducer1;

const Reducer2 = (state={

    currentDepts:{

        a2:"a101",b2:"a102",c2:"a103",d2:"a104"

    }

},action) =>{           

          return Object.assign({},state,{ currentDepts:{a2:"a201",b2:"a202",c2:"a203",d2:"a204"}});

}

export default Reducer2;

Which of the below statements are true?

i. The value of a1 can be modified within Reducer2
ii. The state is shared between Reducer1 and Reducer2

Options:

1. Both i and ii
2. Neither i and ii
3. Only i
4. Only ii

Answer:

2. Neither i and ii

Q20 of 30:

Question: Mily wants to fetch the list of product data from a backend API. Received data will be set as the state of a component i.e. in 'result'. Which of the following code snippets will help her in achieving this requirement? (Assume all required setup is given)

const[result,setResult] = useState("")

axios.get(“api_url”).subscribe(res => setResult(result))

axios.fetch(“api_url”).then(res => setResult({result : res}))

axios.get(“api_url”).then(res => setResult(res.data) )

axios.fetch(“api_url”).then(res => setResult(res.data))

Options:

1. axios.get(“api_url”).subscribe(res => setResult(result))
2. axios.fetch(“api_url”).then(res => setResult({result : res}))
3. axios.get(“api_url”).then(res => setResult(res.data))
4. axios.fetch(“api_url”).then(res => setResult(res.data))

Answer:

3. axios.get(“api_url”).then(res => setResult(res.data))

Q21 of 30:

Question: James, a front-end developer, had a requirement to create a Single Page Application. He decides to create the application using React. Which of the below-listed advantages can James get by using React?

a. Modularity can be achieved by using React JS

b. Optimize DOM manipulation

c. Follows MVC architecture

d. Components can also be created using pure JavaScript

Options:

1. Only a and b are true
2. Only a, c and d are true
3. Only a, b and d are true
4. All the given options are true

Answer:

3. Only a, b, and d are true

Q22 of 30:

Question: Consider the below App component which renders the input field on the UI.

const App = () => {

  const [data, setData] = useState('Initial render');

  return <input type="text" value={data} />;

};

export default App;

Identify the statements which are/is true with respect to the above component. (Select any two)

1. 'Initial render' text will be displayed in the input field.
2. The component is re-rendered when the value is entered in the input field.
3. The value can be typed in the input field.
4. It just displays the blank input field.

Answer:

1. 'Initial render' text will be displayed in the input field.

2. The component is re-rendered when the value is entered in the input field.

Q23 of 30:

Question: Consider the below Route mappings and identify which component will be rendered on encountering the route /.

<Routes>

    <Route path="/" element={<Header />}>

      <Route index element={<Home />} />

      <Route path="home" element={<Home />} />

    </Route>

</Routes>

Options:

1. Header
2. Home
3. Header and Home
4. None of the components will be rendered

Answer:

3. Header and Home

Q24 of 30:

Question: The useEffect() method will run whenever any state of the component changes when there is no second argument passed to it.

Please validate the above statement.

Options:

1. True
2. False

Answer:

2. False

Q25 of 30:

Question: Which of the following statements is true with respect to forms in React?

a. ref is used to give the reference name to the form element.

b. useRef hook returns a ref object.

c. onChange prop must be added to make the form interactive.

Options:

1. Only a
2. Only b
3. Only a & b
4. a, b, c

Answer:

3. Only a & b

Q26 of 30:

Question:

Match the following key points of ReactJS (Set A) with their appropriate options (Set B).

Set A:

a. PascalCasing naming convention

b. className

c. Props

d. React.createElement

Set B:

a. Plain JavaScript

b. Component name

c. class becomes className in JSX

d. Read-Only

Options:

1. a - b, b - c, c - d, d - a
2. a - c, b - b, c - d, d - a
3. a - c, b - a, c - d, d - b
4. a - d, b - c, c - b, d - a

Answer:

3. a - c, b - a, c - d, d - b

Q27 of 30:

Question: Choose the correct statements about the below code:

const [name, setName] = useState('');

const [age, setAge] = useState(0);

useEffect(() => {

  console.log("useEffect method called");

}, [age]);

1. useEffect will be called whenever name and age state changes.
2. useEffect is invoked once after the initial render and then every time when the age state changes.
3. useEffect is invoked once after the initial render.
4. useEffect is not invoked.

Answer:

2. useEffect is invoked once after the initial render and then every time when the age state changes.

Q28 of 30:

Question: Consider the below code written for rendering a submit button of a component.

<Button type="submit"> Submit </Button>

The requirement is to apply the below React-bootstrap styles to the button:

Size of the button - 'small'

Button style - 'primary'

Choose the correct option to achieve the above requirement.

(Assume all required React-bootstrap imports are done)

1. <Button type="submit" style="primary" size="sm"> Submit </Button>
2. <Button type="submit" variant="primary" size="sm"> Submit </Button>
3. <Button type="submit" class="primary" class="sm"> Submit </Button>
4. <Button type="submit" className="primary" className="sm"> Submit </Button>

Answer:

2. <Button type="submit" variant="primary" size="sm"> Submit </Button>

Q29 of 30:

Question: Tom, a React application developer, has created the below component to display examination details for the students.

const ExamDetails = () => {

  return /* Code to display examination details */;

}

And he wants to display the location as Mysore by default if the preferred location is not provided by the student at the form submission time.

Select an appropriate method to be added to the component from the below options.

1. Set default value using defaultProps
2. Set default value using propTypes
3. Use forceUpdate() method and update state as Mysore
4. Set default value using useState hook

Answer:

4. Set default value using useState hook

Q30 of 30:

Question: Sophie is using React Router in her SPA and wants to create a link that can help her to navigate to "/products" URL. Select the appropriate line of code from the below options.

1. <Link href="/products"> Products </Link>
2. <a href="/products"> Products </a>
3. <Link to="/products">Products </Link>
4. <Link path="/products">Products </Link>

Answer:

3. <Link to="/products">Products </Link>