Top 40 ReactJS Coding Interview Questions and Answers

October 24, 2024October 25, 2024 Shailja Kaushik

ReactJS is one of the most popular JavaScript libraries for building user interfaces, particularly for single-page applications. As companies increasingly adopt React for their front-end development, the demand for skilled React developers continues to rise. Preparing for a ReactJS interview requires a strong understanding of coding concepts, problem-solving skills, and practical experience with the library. In this blog, we will cover ReactJS coding interview questions categorized by experience level, followed by a list of the best companies to apply for ReactJS jobs.

Table of Contents

Beginner Level ReactJS Coding Interview Questions and Answers

As a beginner, you will be evaluated on your understanding of basic react JS coding concepts in the interviews. Preparing these foundational topics is essential for building a solid understanding of React before moving on to more complex challenges. We have listed down a few beginner-level reactJS coding interview questions for developers below to help you prepare for your interview.

Q1. Write a simple React component that displays “Hello, World!” on the screen.

Answer: To display “Hello, World” with the help of a React component, we can use the given React code:

import React from 'react';

const HelloWorld = () => {
    return <h1>Hello, World!</h1>;
};

export default HelloWorld;

Q2. Create a functional component that takes a name prop and displays a greeting message.

Answer: To create a functional component that accepts a name prop and displays a greeting message, we can use the following code:

import React from 'react';

const Greeting = ({ name }) => {
    return <h2>Hello, {name}!</h2>;
};

export default Greeting;

Q3. Write a React component that maintains a count state and has buttons to increment and decrement the count.

Answer:This React component maintains a count state and provides buttons for incrementing and decrementing that count:

import React, { useState } from 'react';

const Counter = () => {
    const [count, setCount] = useState(0);
    return (
        <div>
            <h2>Count: {count}</h2>
            <button onClick={() => setCount(count + 1)}>Increment</button>
            <button onClick={() => setCount(count - 1)}>Decrement</button>
        </div>
    );
};

export default Counter;

Q4. How do you create a controlled component for an input field?

Answer: Here’s how we can implement a controlled component for an input field in React:

import React, { useState } from 'react';

const ControlledInput = () => {
    const [value, setValue] = useState('');

    const handleChange = (event) => {
        setValue(event.target.value);
    };

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

export default ControlledInput;

Also Read: Back-End Developer Interview Questions

Q5. Write a simple component that fetches data from an API and displays it.

Answer: This code shows a simple React component that fetches data from an API and displays the results:

import React, { useEffect, useState } from 'react';

const DataFetchingComponent = () => {
    const [data, setData] = useState([]);

    useEffect(() => {
        fetch('https://api.example.com/data')
            .then(response => response.json())
            .then(data => setData(data));
    }, []);

    return (
        <ul>
            {data.map(item => (
                <li key={item.id}>{item.name}</li>
            ))}
        </ul>
    );
};

export default DataFetchingComponent;

Pro Tip: Working on some beginner-friendly react projects can help you understand the basic concepts required to answer such react JS coding interview questions.

Q6. How can you pass data from a parent component to a child component?

Answer: To pass data from a parent component to a child component in React, we can use the following structure:

import React from 'react';

const ChildComponent = ({ message }) => {
    return <h3>{message}</h3>;
};

const ParentComponent = () => {
    const message = "Hello from Parent";

    return <ChildComponent message={message} />;
};

export default ParentComponent;

Q7. Write a component that toggles between two states using a button.

Answer: We can write a React component that toggles between two states using a button with this code:

import React, { useState } from 'react';

const ToggleComponent = () => {
    const [isOn, setIsOn] = useState(false);

    return (
        <div>
            <h2>{isOn ? 'On' : 'Off'}</h2>
            <button onClick={() => setIsOn(!isOn)}>Toggle</button>
        </div>
    );
};

export default ToggleComponent;

Q8. How can you use the useEffect hook to mimic componentDidMount?

Answer: To mimic componentDidMount using the useEffect hook, we can consider this code:

import React, { useEffect } from 'react';

const ComponentDidMountExample = () => {
    useEffect(() => {
        console.log('Component Mounted');
    }, []); // Empty dependency array mimics componentDidMount

    return <h2>Check the console for a message.</h2>;
};

export default ComponentDidMountExample;

Q9. Write a component that displays a list of items and highlights the selected item.

Answer: This component displays a list of items and highlights the selected item based on user interaction:

import React, { useState } from 'react';

const HighlightList = () => {
    const items = ['Item 1', 'Item 2', 'Item 3'];
    const [selectedIndex, setSelectedIndex] = useState(null);

    return (
        <ul>
            {items.map((item, index) => (
                <li 
                    key={index} 
                    onClick={() => setSelectedIndex(index)} 
                    style={{ backgroundColor: selectedIndex === index ? 'yellow' : 'white' }}
                >
                    {item}
                </li>
            ))}
        </ul>
    );
};

export default HighlightList;

Q10. Create a simple form with validation for an email input.

Answer: To create a simple form that includes validation for an email input, we can use the following code:

import React, { useState } from 'react';

const EmailForm = () => {
    const [email, setEmail] = useState('');
    const [error, setError] = useState('');

    const handleSubmit = (event) => {
        event.preventDefault();
        if (!/\S+@\S+\.\S+/.test(email)) {
            setError('Invalid email format');
        } else {
            setError('');
            console.log('Email submitted:', email);
        }
    };

    return (
        <form onSubmit={handleSubmit}>
            <input 
                type="email" 
                value={email} 
                onChange={(e) => setEmail(e.target.value)} 
                placeholder="Enter your email" 
            />
            <button type="submit">Submit</button>
            {error && <p style={{ color: 'red' }}>{error}</p>}
        </form>
    );
};

export default EmailForm;

Mid-Level React Coding Interview Questions and Answers for Developers

In this section, the React JS programming questions are prepared for developers with moderate experience in React. It explores deeper into react concepts. Additionally, topics like logs and react components are discussed at this level of the interview. Candidates are expected to demonstrate their practical coding knowledge and problem-solving skills when dealing with common challenges in React development.

Q11. Write a higher-order component that logs props to the console.

Answer: Through this code, you can create a higher-order component (HOC) that logs the received props before rendering the wrapped component. This is useful for debugging and understanding the data flow in React components.

import React from 'react';

const withLogging = (WrappedComponent) => {
    return (props) => {
        console.log('Props:', props);
        return <WrappedComponent {...props} />;
    };
};

export default withLogging;

Q12. Create a component that uses the useContext hook.

Answer: Here’s a simple code that demonstrates how to utilize the useContext hook in React. This allows components to access context data without having to pass props through every level of the component tree.

import React, { useContext, createContext } from 'react';

const MyContext = createContext();

const ContextProvider = ({ children }) => {
    return <MyContext.Provider value="Hello from Context">{children}</MyContext.Provider>;
};

const ComponentUsingContext = () => {
    const value = useContext(MyContext);
    return <h2>{value}</h2>;
};

const App = () => {
    return (
        <ContextProvider>
            <ComponentUsingContext />
        </ContextProvider>
    );
};

export default App;

Q13. Write a component that fetches data using async/await.

Answer: In this component, you can demonstrate how to fetch data asynchronously using the async/await syntax within a functional component, showcasing the use of the useEffect hook for side effects.

import React, { useEffect, useState } from 'react';

const AsyncFetchComponent = () => {
    const [data, setData] = useState([]);

    useEffect(() => {
        const fetchData = async () => {
            const response = await fetch('https://api.example.com/data');
            const result = await response.json();
            setData(result);
        };
        fetchData();
    }, []);

    return (
        <ul>
            {data.map(item => (
                <li key={item.id}>{item.name}</li>
            ))}
        </ul>
    );
};

export default AsyncFetchComponent;

Also Read: Software Engineer Interview Questions

Q14. Create a component that implements error boundaries.

Answer: This code illustrates how to create an error boundary in React, which catches JavaScript errors in its child component tree and displays a fallback UI.

import React from 'react';

class ErrorBoundary extends React.Component {
    constructor(props) {
        super(props);
        this.state = { hasError: false };
    }

    static getDerivedStateFromError(error) {
        return { hasError: true };
    }

    componentDidCatch(error, errorInfo) {
        console.log('Error logged:', error, errorInfo);
    }

    render() {
        if (this.state.hasError) {
            return <h1>Something went wrong.</h1>;
        }
        return this.props.children; 
    }
}

const FaultyComponent = () => {
    throw new Error('I crashed!');
};

const App = () => {
    return (
        <ErrorBoundary>
            <FaultyComponent />
        </ErrorBoundary>
    );
};

export default App;

Q15. How do you implement debouncing for an input field?

Answer: This component demonstrates how to implement debouncing for an input field, allowing the input value to be updated only after the user stops typing for a specified duration.

import React from 'react';

import React, { useState, useEffect } from 'react';

const DebouncedInput = () => {
    const [value, setValue] = useState('');
    const [debouncedValue, setDebouncedValue] = useState(value);

    useEffect(() => {
        const handler = setTimeout(() => {
            setDebouncedValue(value);
        }, 300);

        return () => {
            clearTimeout(handler);
        };
    }, [value]);

    return (
        <div>
            <input 
                type="text" 
                value={value} 
                onChange={(e) => setValue(e.target.value)} 
                placeholder="Type something..." 
            />
            <p>Debounced Value: {debouncedValue}</p>
        </div>
    );
};

export default DebouncedInput;

Pro Tip: Such kinds of React JS coding interview questions aim to check your knowledge of some core React JS concepts. Preparing for these questions can significantly improve your chances of landing React JS jobs.

Q16. Write a component that uses the useReducer hook.

Answer: This code showcases how to manage complex state logic using the useReducer hook, providing a more structured way to handle state updates than useState.

import React, { useReducer } from 'react';

const initialState = { count: 0 };

const reducer = (state, action) => {
    switch (action.type) {
        case 'increment':
            return { count: state.count + 1 };
        case 'decrement':
            return { count: state.count - 1 };
        default:
            throw new Error();
    }
};

const CounterWithReducer = () => {
    const [state, dispatch] = useReducer(reducer, initialState);

    return (
        <div>
            <h2>Count: {state.count}</h2>
            <button onClick={() => dispatch({ type: 'increment' })}>Increment</button>
            <button onClick={() => dispatch({ type: 'decrement' })}>Decrement</button>
        </div>
    );
};

export default CounterWithReducer;

Q17. Create a custom hook to manage the form input state.

Answer: In this code, you can create a custom hook to handle form input state, which simplifies managing controlled components in forms.

import React, { useState } from 'react';

const useFormInput = (initialValue) => {
    const [value, setValue] = useState(initialValue);

    const handleChange = (event) => {
        setValue(event.target.value);
    };

    return {
        value,
        onChange: handleChange,
    };
};

const CustomForm = () => {
    const nameInput = useFormInput('');

    return (
        <form>
            <input type="text" {...nameInput} placeholder="Name" />
            <button type="submit">Submit</button>
        </form>
    );
};

export default CustomForm;

Q18. Write a component that uses local storage to save form data.

Answer: This component demonstrates how to utilize the browser’s local storage to save and retrieve form data, providing persistence across page reloads.

import React, { useState, useEffect } from 'react';

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

    useEffect(() => {
        const savedName = localStorage.getItem('name');
        if (savedName) {
            setName(savedName);
        }
    }, []);

    const handleSubmit = (event) => {
        event.preventDefault();
        localStorage.setItem('name', name);
        alert('Name saved to local storage!');
    };

    return (
        <form onSubmit={handleSubmit}>
            <input 
                type="text" 
                value={name} 
                onChange={(e) => setName(e.target.value)} 
                placeholder="Enter your name" 
            />
            <button type="submit">Save</button>
        </form>
    );
};

export default LocalStorageForm;

Q19. How do you create a component that uses the useMemo hook?

Answer: This code illustrates how to use the useMemo hook to optimize performance by memoizing expensive calculations based on dependencies.

import React, { useMemo, useState } from 'react';

const MemoizedComponent = () => {
    const [count, setCount] = useState(0);
    const [name, setName] = useState('');

    const computedValue = useMemo(() => {
        console.log('Calculating...');
        return count * 2;
    }, [count]);

    return (
        <div>
            <h2>Count: {count}</h2>
            <h3>Computed Value: {computedValue}</h3>
            <input 
                type="text" 
                value={name} 
                onChange={(e) => setName(e.target.value)} 
                placeholder="Enter your name" 
            />
            <button onClick={() => setCount(count + 1)}>Increment</button>
        </div>
    );
};

export default MemoizedComponent;

Q20. Write a component that implements infinite scrolling.

Answer: This component showcases how to implement infinite scrolling, dynamically loading more content as the user scrolls down the page.

import React, { useState, useEffect } from 'react';

const InfiniteScrollComponent = () => {
    const [items, setItems] = useState([]);
    const [loading, setLoading] = useState(true);
    const [page, setPage] = useState(1);

    const fetchItems = async () => {
        const response = await fetch(`https://api.example.com/items?page=${page}`);
        const newItems = await response.json();
        setItems(prev => [...prev, ...newItems]);
        setLoading(false);
    };

    useEffect(() => {
        fetchItems();
    }, [page]);

    useEffect(() => {
        const handleScroll = () => {
            if (window.innerHeight + document.documentElement.scrollTop >= document.documentElement.offsetHeight) {
                setPage(prev => prev + 1);
            }
        };

        window.addEventListener('scroll', handleScroll);
        return () => window.removeEventListener('scroll', handleScroll);
    }, []);

    return (
        <div>
            <ul>
                {items.map(item => (
                    <li key={item.id}>{item.name}</li>
                ))}
            </ul>
            {loading && <p>Loading...</p>}
        </div>
    );
};

export default InfiniteScrollComponent;

Pro Tip: You can effectively prepare for the React JS coding interview questions by enrolling in a React course. A React course can help you gain practical experience and knowledge of working on basic as well as advanced React JS projects.

Advanced Level ReactJS Tricky Interview Questions

Advanced-level questions are meant for seasoned developers who have extensive experience working with React JS. This section covers topics like code optimization, React performance tuning, and techniques such as code-splitting and lazy loading to improve efficiency. There may also be tricky questions related to server-side rendering (SSR) with Next.js, managing large-scale applications, and dealing with state management libraries like Redux or Recoil. This section tests the candidate’s ability to solve complex problems and handle real-world challenges in React development.

Q21. Write a component that uses the React. memo for optimization.

Answer: In this code, we can see how to use React.memo to prevent unnecessary re-renders of a child component. This is particularly useful when the parent component re-renders frequently, allowing the child component to remain unchanged if its props have not changed.

import React from 'react';

const ChildComponent = React.memo(({ name }) => {
    console.log('ChildComponent rendered');
    return <h3>{name}</h3>;
});

const ParentComponent = () => {
    const [count, setCount] = React.useState(0);
    const name = 'John Doe';

    return (
        <div>
            <h2>Count: {count}</h2>
            <ChildComponent name={name} />
            <button onClick={() => setCount(count + 1)}>Increment</button>
        </div>
    );
};

export default ParentComponent;

Pro Tip: A roadmap can prove to be beneficial while preparing for a career in the domain of React JS. You can check out the ultimate React roadmap to prepare effectively for React JS coding interviews.

Q22. Create a component that demonstrates the use of refs.

Answer: This code illustrates how to use the useRef hook to create a reference to a DOM element, allowing us to programmatically focus an input field when a button is clicked.

import React, { useRef } from 'react';

const RefExample = () => {
    const inputRef = useRef();

    const focusInput = () => {
        inputRef.current.focus();
    };

    return (
        <div>
            <input ref={inputRef} type="text" placeholder="Focus me!" />
            <button onClick={focusInput}>Focus Input</button>
        </div>
    );
};

export default RefExample;

Q23. How do you implement a custom context provider?

Answer: In this code, we will create a custom context provider using React’s Context API. This provider allows us to manage and share state across multiple components without prop drilling.

import React, { createContext, useContext, useState } from 'react';

const MyContext = createContext();

const MyProvider = ({ children }) => {
    const [state, setState] = useState('Default Value');

    return (
        <MyContext.Provider value={{ state, setState }}>
            {children}
        </MyContext.Provider>
    );
};

const MyComponent = () => {
    const { state, setState } = useContext(MyContext);
    return (
        <div>
            <h2>{state}</h2>
            <button onClick={() => setState('New Value')}>Change Value</button>
        </div>
    );
};

const App = () => {
    return (
        <MyProvider>
            <MyComponent />
        </MyProvider>
    );
};

export default App;

Q24. Create a component that shows how to use portals.

Answer: This code demonstrates how to create a modal using React portals. Portals provide a way to render children into a DOM node that exists outside the hierarchy of the parent component.

import React from 'react';
import ReactDOM from 'react-dom';

const Modal = ({ children }) => {
    return ReactDOM.createPortal(
        <div style={{ background: 'rgba(0,0,0,0.7)', padding: '20px' }}>
            <h2>Modal</h2>
            {children}
        </div>,
        document.getElementById('modal-root')
    );
};

const App = () => {
    return (
        <div>
            <h1>Main App</h1>
            <Modal>
                <p>This is a modal!</p>
            </Modal>
        </div>
    );
};

export default App;

Also Read: Full Stack Interview Questions

Q25. How can you use the useLayoutEffect hook?

Answer: Here, we will illustrate the use of the useLayoutEffect hook to measure the window size immediately after the DOM is updated, allowing us to perform side effects based on the layout of the components.

import React, { useLayoutEffect, useState } from 'react';

const LayoutEffectExample = () => {
    const [size, setSize] = useState(window.innerWidth);

    useLayoutEffect(() => {
        const handleResize = () => {
            setSize(window.innerWidth);
        };

        window.addEventListener('resize', handleResize);
        return () => {
            window.removeEventListener('resize', handleResize);
        };
    }, []);

    return <h2>Window Size: {size}</h2>;
};

export default LayoutEffectExample;

Q26. Write a react component that utilizes error boundaries.

Answer: In this code, an error boundary that logs props before rendering the wrapped component is created. Error boundaries are essential for catching JavaScript errors in components and displaying a fallback UI.

import React from 'react';

const withLogging = (WrappedComponent) => {
    return (props) => {
        console.log('Props:', props);
        return <WrappedComponent {...props} />;
    };
};

export default withLogging;

Pro Tip: Questions around react components are asked commonly in React JS interviews. You can learn about React components in order to answer such React JS programming interview questions.

Q27. How do you implement a dynamic import in a React component?

Answer: This code demonstrates how to implement dynamic imports using React.lazy and Suspense, allowing us to load components lazily, and improving the initial load time of our application.

import React, { Suspense, useState } from 'react';

const LazyComponent = React.lazy(() => import('./LazyComponent'));

const App = () => {
    const [show, setShow] = useState(false);

    return (
        <div>
            <button onClick={() => setShow(!show)}>Toggle Lazy Component</button>
            <Suspense fallback={<div>Loading...</div>}>
                {show && <LazyComponent />}
            </Suspense>
        </div>
    );
};

export default App;

Q28. Create a component that demonstrates how to handle fetch requests with error handling.

Answer: In this example, we handle fetch requests and implement error handling using the useEffect hook. This approach ensures that any network issues are gracefully handled, providing feedback to the user.

import React, { useState, useEffect } from 'react';

const FetchExample = () => {
    const [data, setData] = useState(null);
    const [error, setError] = useState(null);

    useEffect(() => {
        const fetchData = async () => {
            try {
                const response = await fetch('https://api.example.com/data');
                if (!response.ok) {
                    throw new Error('Network response was not ok');
                }
                const result = await response.json();
                setData(result);
            } catch (error) {
                setError(error.message);
            }
        };

        fetchData();
    }, []);

    if (error) {
        return <div>Error: {error}</div>;
    }

    return <div>{data ? JSON.stringify(data) : 'Loading...'}</div>;
};

export default FetchExample;

Q29. How do you implement a loading spinner while fetching data?

Answer: This code showcases a simple loading spinner that is displayed while data is being fetched from an API. It enhances user experience by indicating that data is being loaded.

import React, { useState, useEffect } from 'react';

const LoadingSpinner = () => {
    return <div>Loading...</div>;
};

const DataFetchingComponent = () => {
    const [data, setData] = useState(null);
    const [loading, setLoading] = useState(true);

    useEffect(() => {
        const fetchData = async () => {
            const response = await fetch('https://api.example.com/data');
            const result = await response.json();
            setData(result);
            setLoading(false);
        };

        fetchData();
    }, []);

    if (loading) {
        return <LoadingSpinner />;
    }

    return <div>{JSON.stringify(data)}</div>;
};

export default DataFetchingComponent;

Q30. How do you optimize performance using the use callback hook?

Answer: In this code, we use the useCallback hook to memoize callback functions, preventing unnecessary re-renders of components that depend on those functions.

import React, { useCallback, useState } from 'react';

const Counter = React.memo(({ increment }) => {
    console.log('Counter rendered');
    return <button onClick={increment}>Increment</button>;
});

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

    const increment = useCallback(() => {
        setCount(prevCount => prevCount + 1);
    }, []);

    return (
        <div>
            <h2>Count: {count}</h2>
            <Counter increment={increment} />
        </div>
    );
};

export default App;

ReactJS Technical Interview Questions for Developers

This section includes various ReactJS technical questions with answers that span from the basics to more advanced concepts in ReactJS. The questions help candidates reinforce their knowledge of React’s component architecture, lifecycle methods, and state management. As the difficulty level progresses, developers will encounter more challenging topics like context API, hooks in React, error boundaries, and React patterns. This section aims to prepare candidates comprehensively, whether they are freshers or experienced professionals looking to refresh their skills.

Q31. Write a simple React component that takes props.

Answer: This component, Greeting, takes a name prop and displays a greeting message.

import React from 'react';

const Greeting = ({ name }) => {
    return <h1>Hello, {name}!</h1>;
};

export default Greeting;

Q32. How do you pass data from a child component to a parent component?

Answer: In this code, the Child component sends data back to the Parent component using a callback function passed as a prop.

import React, { useState } from 'react';

const Child = ({ onSendData }) => {
    const handleClick = () => {
        onSendData('Data from Child');
    };

    return <button onClick={handleClick}>Send Data to Parent</button>;
};

const Parent = () => {
    const [data, setData] = useState('');

    return (
        <div>
            <h2>Received: {data}</h2>
            <Child onSendData={setData} />
        </div>
    );
};

export default Parent;

Q33. Write a code for a component that uses props to customize styling.

Answer: This StyledComponent demonstrates how to customize styles dynamically using a color prop.

import React from 'react';

const StyledComponent = ({ color }) => {
    return <div style={{ color }}>This is a styled component!</div>;
};

export default StyledComponent;

Q34. How do you handle events in React? Explain with a code.

Answer: In this EventHandlingComponent, a button click triggers an alert, showcasing how to handle events in React.

import React from 'react';

const EventHandlingComponent = () => {
    const handleClick = () => {
        alert('Button clicked!');
    };

    return <button onClick={handleClick}>Click Me</button>;
};

export default EventHandlingComponent;

Q35. Create a simple controlled component.

Answer: The ControlledInput component given in this code maintains its input state with the help of the useState hook, ensuring the input value is controlled by React.

import React, { useState } from 'react';

const ControlledInput = () => {
    const [value, setValue] = useState('');

    const handleChange = (e) => {
        setValue(e.target.value);
    };

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

export default ControlledInput;

Q36. Write a functional component with state.

Answer: This CounterComponent demonstrates state management using the useState hook to update and display a count value.

import React, { useState } from 'react';

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

    return (
        <div>
            <h2>Count: {count}</h2>
            <button onClick={() => setCount(count + 1)}>Increment</button>
        </div>
    );
};

export default CounterComponent;

Q37. How do you implement conditional rendering in React?

Answer: In this ConditionalRenderingComponent, the visibility of an element is toggled based on the state, showcasing conditional rendering.

import React, { useState } from 'react';

const ConditionalRenderingComponent = () => {
    const [isVisible, setIsVisible] = useState(true);

    return (
        <div>
            {isVisible && <h2>This is visible</h2>}
            <button onClick={() => setIsVisible(!isVisible)}>
                Toggle Visibility
            </button>
        </div>
    );
};

export default ConditionalRenderingComponent;

Q38. Create a component that uses effect hooks.

Answer: The EffectComponent utilizes the useEffect hook to log changes to the count state whenever it updates.

import React, { useEffect, useState } from 'react';

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

    useEffect(() => {
        console.log(`Count updated: ${count}`);
    }, [count]);

    return (
        <div>
            <h2>Count: {count}</h2>
            <button onClick={() => setCount(count + 1)}>Increment</button>
        </div>
    );
};

export default EffectComponent;

Q39. How do you create a form with controlled components?

Answer: This FormComponent demonstrates a controlled form where the input state is managed using React, displaying an alert upon submission.

import React, { useState } from 'react';

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

    const handleSubmit = (e) => {
        e.preventDefault();
        alert(`Name: ${name}`);
    };

    return (
        <form onSubmit={handleSubmit}>
            <input 
                type="text" 
                value={name} 
                onChange={(e) => setName(e.target.value)} 
                placeholder="Enter your name" 
            />
            <button type="submit">Submit</button>
        </form>
    );
};

export default FormComponent;

Q40. Write a simple React component that demonstrates lifecycle methods.

Answer: The lifecycleExample class component mentioned in the code below showcases lifecycle methods such as componentDidMount, componentDidUpdate, and componentWillUnmount.

import React, { Component } from 'react';

class LifecycleExample extends Component {
    constructor(props) {
        super(props);
        this.state = { count: 0 };
    }

    componentDidMount() {
        console.log('Component mounted');
    }

    componentDidUpdate() {
        console.log('Component updated');
    }

    componentWillUnmount() {
        console.log('Component will unmount');
    }

    increment = () => {
        this.setState({ count: this.state.count + 1 });
    };

    render() {
        return (
            <div>
                <h2>Count: {this.state.count}</h2>
                <button onClick={this.increment}>Increment</button>
            </div>
        );
    }
}

export default LifecycleExample;

Best Companies to Apply for ReactJS Jobs

Below is a table of some of the best companies to apply for ReactJS positions, along with their average salary ranges:

Company Name	Average Salary (Per Annum)
Google	₹12 LPA – ₹20 LPA
Microsoft	₹10 LPA – ₹18 LPA
Amazon	₹9 LPA – ₹15 LPA
Facebook	₹11 LPA – ₹22 LPA
IBM	₹8 LPA – ₹16 LPA
Accenture	₹7 LPA – ₹14 LPA
Infosys	₹6 LPA – ₹12 LPA
TCS	₹6 LPA – ₹11 LPA
Wipro	₹6.5 LPA – ₹13 LPA
Capgemini	₹7 LPA – ₹14 LPA

Conclusion

A ReactJS interview can be a bit challenging, but with the right knowledge and practice, you can successfully land a job. This blog covered essential React JS coding interview questions and answers across various difficulty levels, from beginner to advanced. All of these questions are commonly asked in React JS interviews. By mastering these concepts and sample answers, you’ll be well-equipped to demonstrate your skills to potential employers.

FAQs

Q1. What is React JS, and why is it popular?

Answer: React JS is a JavaScript library for building user interfaces, particularly single-page applications. Its popularity stems from its component-based architecture, efficiency, and ability to create dynamic, high-performance web applications.

Q2. How do you prepare for a React JS interview?

Answer: To prepare for a React JS interview, practice coding challenges, and review key concepts like hooks, state management, and component lifecycle. Familiarize yourself with common interview questions and build projects using React to enhance your practical skills.

Q3. What are some essential React JS concepts to study?

Answer: The key React JS concepts include JSX, components (functional and class-based), props, state, lifecycle methods, hooks (useState, useEffect), context API, and error boundaries.

Q4. What should you expect during a React JS coding interview?

Answer: You can expect to solve coding problems related to component creation, state management, handling events, and optimizing performance. Interviews may include live coding sessions or take-home assignments.

Q5. Are there any resources for learning React JS?

Answer: Yes, there are many resources available, including the official React documentation, online courses available on Internshala trainings, YouTube tutorials, and books focused on React development.