Live Coding React Interview Questions

React is one of the most popular libraries for building user interfaces. It's no surprise that React developers are in high demand. If you're preparing for a React interview, live coding challenges are an essential part of the process. These challenges test your understanding of React concepts, your problem-solving skills, and your ability to write clean, efficient code.

In this blog post, we'll cover 20 advanced React coding challenges that can help you ace your next interview. Each challenge includes a problem description and an example solution to help you understand the concept better. Let's dive in!

Table of Contents

1. Create a Counter Component
2. Implement a Toggle Switch
3. Build a To-Do List
4. Fetch Data from an API
5. Create a Search Bar
6. Build a Dropdown Menu
7. Implement a Tabs Component
8. Create a Modal Component
9. Build a Carousel Component
10. Implement a Star Rating Component
11. Create a Real-Time Search Filter
12. Build a Multi-Step Form
13. Implement a Virtualized List
14. Create a Reusable Form Component with Validation
15. Implement a Dynamic Form with Field Arrays
16. Implement a Context API for Global State
17. Create a Custom Hook
18. Build a Todo List with Drag-and-Drop
19. Create a Countdown Timer
20. Implement Formik with Yup Validation Conclusion

1. Create a Counter Component.

Problem:
Create a simple counter component that increases or decreases the count when clicking buttons.

Solution:

import React, { useState } from 'react';

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

  return (
    <div>
      <p>Count: {count}</p>
      <button onClick={() => setCount(count + 1)}>Increase</button>
      <button onClick={() => setCount(count - 1)}>Decrease</button>
    </div>
  );
};

export default Counter;

2. Implement a Toggle Switch

Problem:
Create a toggle switch component between "On" and "Off" states.
Solution:

import React, { useState } from 'react';

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

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

export default ToggleSwitch;

3. Build a To-Do List

Problem:
Create a to-do list component where users can add, remove, and mark items as complete.
Solution:

import React, { useState } from 'react';

const TodoList = () => {
  const [todos, setTodos] = useState([]);
  const [text, setText] = useState('');

  const addTodo = () => {
    if (text) {
      setTodos([...todos, { text, completed: false }]);
      setText('');
    }
  };

  const toggleTodo = index => {
    const newTodos = [...todos];
    newTodos[index].completed = !newTodos[index].completed;
    setTodos(newTodos);
  };

  const removeTodo = index => {
    const newTodos = [...todos];
    newTodos.splice(index, 1);
    setTodos(newTodos);
  };

  return (
    <div>
      <input value={text} onChange={(e) => setText(e.target.value)} placeholder="Add a to-do" />
      <button onClick={addTodo}>Add</button>
      <ul>
        {todos.map((todo, index) => (
          <li key={index} style={{ textDecoration: todo.completed ? 'line-through' : 'none' }}>
            {todo.text}
            <button onClick={() => toggleTodo(index)}>Toggle</button>
            <button onClick={() => removeTodo(index)}>Remove</button>
          </li>
        ))}
      </ul>
    </div>
  );
};

export default TodoList;

4. Fetch Data from an API

Problem:
Create a component fetching data from an API and displaying it in a list.
Solution:

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

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

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

  if (loading) return <p>Loading...</p>;

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

export default DataFetcher;

5. Create a Search Bar

Problem:
Create a search bar component that filters a list of items as the user types.
Solution:

import React, { useState } from 'react';

const SearchBar = ({ items }) => {
  const [query, setQuery] = useState('');

  const filteredItems = items.filter(item =>
    item.toLowerCase().includes(query.toLowerCase())
  );

  return (
    <div>
      <input
        type="text"
        value={query}
        onChange={e => setQuery(e.target.value)}
        placeholder="Search..."
      />
      <ul>
        {filteredItems.map((item, index) => (
          <li key={index}>{item}</li>
        ))}
      </ul>
    </div>
  );
};

const App = () => {
  const items = ['Apple', 'Banana', 'Cherry', 'Date', 'Elderberry'];

  return <SearchBar items={items} />;
};

export default App;

6. Build a Dropdown Menu

Problem:
Create a dropdown menu component that displays a list of items when clicked.
Solution:

import React, { useState } from 'react';

const DropdownMenu = ({ items }) => {
  const [isOpen, setIsOpen] = useState(false);

  return (
    <div>
      <button onClick={() => setIsOpen(!isOpen)}>Menu</button>
      {isOpen && (
        <ul>
          {items.map((item, index) => (
            <li key={index}>{item}</li>
          ))}
        </ul>
      )}
    </div>
  );
};

const App = () => {
  const items = ['Profile', 'Settings', 'Logout'];

  return <DropdownMenu items={items} />;
};

export default App;

7. Implement a Tabs Component

Problem:
Create a tabs component where each tab displays different content when selected.
Solution:

import React, { useState } from 'react';

const Tabs = ({ tabs }) => {
  const [activeTab, setActiveTab] = useState(0);

  return (
    <div>
      <div className="tab-buttons">
        {tabs.map((tab, index) => (
          <button
            key={index}
            className={index === activeTab ? 'active' : ''}
            onClick={() => setActiveTab(index)}
          >
            {tab.label}
          </button>
        ))}
      </div>
      <div className="tab-content">
        {tabs[activeTab].content}
      </div>
    </div>
  );
};

const App = () => {
  const tabs = [
    { label: 'Tab 1', content: <div>Content of Tab 1</div> },
    { label: 'Tab 2', content: <div>Content of Tab 2</div> },
    { label: 'Tab 3', content: <div>Content of Tab 3</div> },
  ];

  return <Tabs tabs={tabs} />;
};

export default App;

8. Create a Modal Component

Problem:
Create a reusable modal component that can be opened and closed and display any content passed to it.
Solution:

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

const Modal = ({ isOpen, onClose, children }) => {
  useEffect(() => {
    if (isOpen) {
      document.body.style.overflow = 'hidden';
    } else {
      document.body.style.overflow = 'auto';
    }
  }, [isOpen]);

  if (!isOpen) return null;

  return ReactDOM.createPortal(
    <div className="modal-overlay" onClick={onClose}>

 <div className="modal-content" onClick={e => e.stopPropagation()}>
        <button className="modal-close" onClick={onClose}>Close</button>
        {children}
      </div>
    </div>,
    document.body
  );
};

const App = () => {
  const [isModalOpen, setIsModalOpen] = useState(false);

  return (
    <div>
      <button onClick={() => setIsModalOpen(true)}>Open Modal</button>
      <Modal isOpen={isModalOpen} onClose={() => setIsModalOpen(false)}>
        <h1>Modal Content</h1>
        <p>This is the content inside the modal</p>
      </Modal>
    </div>
  );
};

export default App;

9. Build a Carousel Component

Problem:
Create a carousel component that cycles through a set of images.
Solution:

import React, { useState } from 'react';

const Carousel = ({ images }) => {
  const [currentIndex, setCurrentIndex] = useState(0);

  const goToNext = () => {
    setCurrentIndex((currentIndex + 1) % images.length);
  };

  const goToPrevious = () => {
    setCurrentIndex((currentIndex - 1 + images.length) % images.length);
  };

  return (
    <div className="carousel">
      <button onClick={goToPrevious}>Previous</button>
      <img src={images[currentIndex]} alt="carousel" />
      <button onClick={goToNext}>Next</button>
    </div>
  );
};

const App = () => {
  const images = [
    'https://via.placeholder.com/600x400?text=Image+1',
    'https://via.placeholder.com/600x400?text=Image+2',
    'https://via.placeholder.com/600x400?text=Image+3',
  ];

  return <Carousel images={images} />;
};

export default App;

10. Implement a Star Rating Component

Problem:
Create a star rating component where users can rate something from 1 to 5 stars.
Solution:

import React, { useState } from 'react';

const StarRating = ({ totalStars = 5 }) => {
  const [rating, setRating] = useState(0);

  return (
    <div>
      {[...Array(totalStars)].map((star, index) => {
        const starValue = index + 1;
        return (
          <span
            key={index}
            onClick={() => setRating(starValue)}
            style={{ cursor: 'pointer', color: starValue <= rating ? 'gold' : 'gray' }}
          >
            ★
          </span>
        );
      })}
    </div>
  );
};

const App = () => {
  return (
    <div>
      <h1>Star Rating</h1>
      <StarRating />
    </div>
  );
};

export default App;

11. Create a Real-Time Search Filter

Problem:
Create a search filter component that filters a list of items in real-time as the user types.
Solution:

import React, { useState } from 'react';

const RealTimeSearch = ({ items }) => {
  const [query, setQuery] = useState('');

  const filteredItems = items.filter(item =>
    item.toLowerCase().includes(query.toLowerCase())
  );

  return (
    <div>
      <input
        type="text"
        value={query}
        onChange={e => setQuery(e.target.value)}
        placeholder="Search..."
      />
      <ul>
        {filteredItems.map((item, index) => (
          <li key={index}>{item}</li>
        ))}
      </ul>
    </div>
  );
};

const App = () => {
  const items = ['Apple', 'Banana', 'Cherry', 'Date', 'Elderberry'];

  return <RealTimeSearch items={items} />;
};

export default App;

12. Build a Multi-Step Form

Problem:
Create a multi-step form where users can navigate between different steps of the form.
Solution:

import React, { useState } from 'react';

const Step1 = ({ next }) => (
  <div>
    <h2>Step 1</h2>
    <button onClick={next}>Next</button>
  </div>
);

const Step2 = ({ next, previous }) => (
  <div>
    <h2>Step 2</h2>
    <button onClick={previous}>Previous</button>
    <button onClick={next}>Next</button>
  </div>
);

const Step3 = ({ previous }) => (
  <div>
    <h2>Step 3</h2>
    <button onClick={previous}>Previous</button>
    <button type="submit">Submit</button>
  </div>
);

const MultiStepForm = () => {
  const [step, setStep] = useState(1);

  const nextStep = () => setStep(step + 1);
  const previousStep = () => setStep(step - 1);

  const handleSubmit = (e) => {
    e.preventDefault();
    console.log('Form submitted');
  };

  return (
    <form onSubmit={handleSubmit}>
      {step === 1 && <Step1 next={nextStep} />}
      {step === 2 && <Step2 next={nextStep} previous={previousStep} />}
      {step === 3 && <Step3 previous={previousStep} />}
    </form>
  );
};

const App = () => {
  return (
    <div>
      <h1>Multi-Step Form</h1>
      <MultiStepForm />
    </div>
  );
};

export default App;

13. Implement a Virtualized List

Problem:
Create a virtualized list component that efficiently renders a large list of items, only rendering items that are visible within the viewport.

Solution:

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

const VirtualizedList = ({ items, itemHeight, height }) => {
  const [scrollTop, setScrollTop] = useState(0);
  const totalHeight = items.length * itemHeight;
  const viewportRef = useRef(null);

  const handleScroll = () => {
    setScrollTop(viewportRef.current.scrollTop);
  };

  const startIndex = Math.floor(scrollTop / itemHeight);
  const endIndex = Math.min(items.length - 1, startIndex + Math.ceil(height / itemHeight));

  const visibleItems = items.slice(startIndex, endIndex + 1).map((item, index) => (
    <div key={index} style={{ height: itemHeight }}>
      {item}
    </div>
  ));

  return (
    <div ref={viewportRef} onScroll={handleScroll} style={{ height, overflowY: 'auto', position: 'relative' }}>
      <div style={{ height: totalHeight, position: 'relative' }}>
        <div style={{ position: 'absolute', top: startIndex * itemHeight, width: '100%' }}>
          {visibleItems}
        </div>
      </div>
    </div>
  );
};

const App = () => {
  const items = Array.from({ length: 1000 }, (_, i) => `Item ${i + 1}`);

  return (
    <div>
      <VirtualizedList items={items} itemHeight={50} height={400} />
    </div>
  );
};

export default App;

14. Create a Reusable Form Component with Validation

Problem:
Build a reusable form component that handles form state and validation for various form fields.
Solution:

import React, { useState } from 'react';

const useForm = (initialValues, validate) => {
  const [values, setValues] = useState(initialValues);
  const [errors, setErrors] = useState({});

  const handleChange = (e) => {
    const { name, value } = e.target;
    setValues({ ...values, [name]: value });

    const error = validate({ [name]: value });
    setErrors({ ...errors, [name]: error[name] });
  };

  const handleSubmit = (callback) => (e) => {
    e.preventDefault();
    const validationErrors = validate(values);
    setErrors(validationErrors);

    if (Object.keys(validationErrors).length === 0) {
      callback();
    }
  };

  return { values, errors, handleChange, handleSubmit };
};

const Form = ({ onSubmit }) => {
  const initialValues = { username: '', email: '' };

  const validate = (values) => {
    const errors = {};
    if (!values.username) {
      errors.username = 'Username is required';
    }
    if (!values.email) {
      errors.email = 'Email is required';
    } else if (!/\S+@\S+\.\S+/.test(values.email)) {
      errors.email = 'Email is invalid';
    }
    return errors;
  };

  const { values, errors, handleChange, handleSubmit } = useForm(initialValues, validate);

  return (
    <form onSubmit={handleSubmit(() => onSubmit(values))}>
      <div>
        <label>Username</label>
        <input name="username" value={values.username} onChange={handleChange} />
        {errors.username && <p>{errors.username}</p>}
      </div>
      <div>
        <label>Email</label>
        <input name="email" value={values.email} onChange={handleChange} />
        {errors.email && <p>{errors.email}</p>}
      </div>
      <button type="submit">Submit</button>
    </form>
  );
};

const App = () => {
  const handleSubmit = (values) => {
    console.log('Form Submitted:', values);
  };

  return (
    <div>
      <h1>Reusable Form</h1>
      <Form onSubmit={handleSubmit} />
    </div>
  );
};

export default App;

15. Implement a Dynamic Form with Field Arrays

Problem:
Create a dynamic form that allows users to add or remove fields dynamically.
Solution:

import React, { useState } from 'react';

const DynamicForm = () => {
  const [fields, setFields] = useState([{ value: '' }]);

  const handleChange = (index, event) => {
    const newFields = fields.slice();
    newFields[index].value = event.target.value;
    setFields(newFields);
  };

  const handleAdd = () => {
    setFields([...fields, { value: '' }]);
  };

  const handleRemove = (index) => {
    const newFields = fields.slice();
    newFields.splice(index, 1);
    setFields(newFields);
  };

  const handleSubmit = (e) => {
    e.preventDefault();
    console.log('Form submitted:', fields);
  };

  return (
    <form onSubmit={handleSubmit}>
      {fields.map((field, index) => (
        <div key={index}>
          <input
            type="text"
            value={field.value}
            onChange={(e) => handleChange(index, e)}
          />
          <button type="button" onClick={() => handleRemove(index)}>Remove</button>
        </div>
      ))}
      <button type="button" onClick={handleAdd}>Add Field</button>
      <button type="submit">Submit</button>
    </form>
  );
};

const App = () => {
  return (
    <div>
      <h1>Dynamic Form</h1>
      <DynamicForm />
    </div>
  );
};

export default App;

16. Implement a Context API for Global State

Problem:
Create a global state using React's Context API to manage the state of posts across the application.
Solution:

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

// Create a Context for the posts
const PostsContext = createContext();

// Define a reducer to manage the state of posts
const postsReducer = (state, action) => {
  switch (action.type) {
    case 'ADD_POST':
      return [...state, action.payload];
    case 'REMOVE_POST':
      return state.filter((post, index) => index !== action.payload);
    default:
      return state;
  }
};

// Create a provider component
const PostsProvider = ({ children }) => {
  const [posts, dispatch] = useReducer(postsReducer, []);

  return (
    <PostsContext.Provider value={{ posts, dispatch }}>
      {children}
    </PostsContext.Provider>
  );
};

// Create a custom hook to use the PostsContext
const usePosts = () => {
  return useContext(PostsContext);
};

const App = () => {
  const { posts, dispatch } = usePosts();

  const addPost = () => {
    dispatch({ type: 'ADD_POST', payload: 'New Post' });
  };

  const removePost = (index) => {
    dispatch({ type: 'REMOVE_POST', payload: index });
  };

  return (
    <div>
      <button onClick={addPost}>Add Post</button>
      <ul>
        {posts.map((post, index) => (
          <li key={index}>
            {post} <button onClick={() => removePost(index)}>Remove</button>
          </li>
        ))}
      </ul>
    </div>
  );
};

const Root = () => (
  <PostsProvider>
    <App />
  </PostsProvider>
);

export default Root;

17. Create a Custom Hook

Problem:
Create a custom hook that fetches and caches data from an API.
Solution:

import { useState, useEffect } from 'react';

const useFetch = (url) => {
  const [data, setData] = useState(null);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState(null);

  useEffect(() => {
    let isMounted = true;
    fetch(url)
      .then((response) => response.json())
      .then((data) => {
        if (isMounted) {
          setData(data);
          setLoading(false);
        }
      })
      .catch((error) => {
        if (isMounted) {
          setError(error);
          setLoading(false);
        }
      });

    return () => {
      isMounted = false;
    };
  }, [url]);

  return { data, loading, error };
};

const App = () => {
  const { data, loading, error } = useFetch('https://api.example.com/data');

  if (loading) return <p>Loading...</p>;
  if (error) return <p>Error: {error.message}</p>;

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

export default App;

18. Build a Todo List with Drag-and-Drop

Problem:
Create a todo list application with drag-and-drop functionality to reorder items.

Solution:

import React, { useState } from 'react';
import { DragDropContext, Droppable, Draggable } from 'react-beautiful-dnd';

const TodoList = () => {
  const [todos, setTodos] = useState([
    'Learn React',
    'Learn Redux',
    'Build a React App',
  ]);

  const handleOnDragEnd = (result) => {
    if (!result.destination) return;

    const reorderedTodos = Array.from(todos);
    const [removed] = reorderedTodos.splice(result.source.index, 1);
    reorderedTodos.splice(result.destination.index, 0, removed);

    setTodos(reorderedTodos);
  };

  return (
    <DragDropContext onDragEnd={handleOnDragEnd}>
      <Droppable droppableId="todos">
        {(provided) => (
          <ul {...provided.droppableProps} ref={provided.innerRef}>
            {todos.map((todo, index) => (
              <Draggable key={todo} draggableId={todo} index={index}>
                {(provided) => (
                  <li ref={provided.innerRef} {...provided.draggableProps} {...provided.dragHandleProps}>
                    {todo}
                  </li>
                )}
              </Draggable>
            ))}
            {provided.placeholder}
          </ul>
        )}
      </Droppable>
    </DragDropContext>
  );
};

const App = () => {
  return (
    <div>
      <h1>Todo List with Drag-and-Drop</h1>
      <TodoList />
    </div>
  );
};

export default App;

19. Create a Countdown Timer

Problem:
Create a countdown timer component that counts down from a given time.
Solution:

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

const CountdownTimer = ({ initialSeconds }) => {
  const [seconds, setSeconds] = useState(initialSeconds);

  useEffect(() => {
    const timer = setInterval(() => {
      setSeconds((prevSeconds) => prevSeconds - 1);
    }, 1000);

    return () => clearInterval(timer);
  }, []);

  return (
    <div>
      <h1>Countdown Timer</h1>
      <p>{seconds} seconds remaining</p>
    </div>
  );
};

const App = () => {
  return (
    <div>
      <CountdownTimer initialSeconds={60} />
    </div>
  );
};

export default App;

20. Implement Formik with Yup Validation

Problem:
Create a form with validation using Formik and Yup.
Solution:

import React from 'react';
import { Formik, Form, Field, ErrorMessage } from 'formik';
import * as Yup from 'yup';

const validationSchema = Yup.object().shape({
  username: Yup.string().required('Username is required'),
  email: Yup.string().email('Invalid email').required('Email is required'),
});

const App = () => {
  return (
    <div>
      <h1>Formik Form with Yup Validation</h1>
      <Formik
        initialValues={{ username: '', email: '' }}
        validationSchema={validationSchema}
        onSubmit={(values) => {
          console.log('Form Submitted', values);
        }}
      >
        {() => (
          <Form>
            <div>
              <label>Username</label>
              <Field name="username" />
              <ErrorMessage name="username" component="div" />
            </div>
            <div>
              <label>Email</label>
              <Field name="email" type="email" />
              <ErrorMessage name="email" component="div" />
            </div>
            <button type="submit">Submit</button>
          </Form>
        )}
      </Formik>
    </div>
  );
};

export default App;

Conclusion

These coding challenges cover various React concepts and techniques, from state management and hooks to custom components and libraries. Each challenge provides a problem and a solution, helping you build practical skills that can be applied in real-world projects. Whether preparing for an interview or just looking to improve your React knowledge, these challenges are a great way to practice and learn. Happy coding!