3 Major Asked Differences in ReactJS Interview — Interview Questions

In this story, we will understand those 3 major differences in ReactJS that are being asked in almost every interview of ReactJS from beginner to senior level.

1. Difference between Stateful and Stateless Components

Stateful Components

• Stateful components, also known as class components, can hold and manage their local state.
• They can modify their state using the setState() method, triggering re-renders when the state changes.
• Stateful components are typically used when the component needs to maintain and update its state over time, handle user interactions, or manage complex logic.

Example:

import React, { Component } from 'react';

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

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

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

export default Counter;        

Stateless Components

• Stateless components, also known as functional components, do not have an internal state.
• They are primarily used for presentational purposes, receiving data via props and rendering UI based on that data.
• Stateless components are simpler and more lightweight than stateful components, as they do not manage any state internally.
• In Stateless components, we need to use “useState()” hook to utilize the state in the component.

Example:

import React, { useState } from 'react';

const MyComponent = () => {
  // Using useState hook to declare state variables
  const [count, setCount] = useState(0);

  const incrementCount = () => {
    setCount(count + 1);
  };

  return (
    <div>
      <p>Count: {count}</p>
      <button onClick={incrementCount}>Increment</button>
    </div>
  );
};

export default MyComponent;        

2. Difference between Controlled and Un-Controlled Components

Controlled Components

• In controlled components, form data is handled by the React component state.
• The value of the form elements (like input, textarea, select) is controlled by the React component state.
• Whenever the user inputs data, the state is updated, and the component re-renders with the new value.
• Controlled components provide more control over the form data and allow for validation and manipulation before updating the state.

Example:

import React, { useState } from 'react';

function ControlledComponentExample() {
  const [inputValue, setInputValue] = useState('');

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

  return (
    <div>
      <input
        type="text"
        value={inputValue}
        onChange={handleChange}
      />
      <p>Input value: {inputValue}</p>
    </div>
  );
}

export default ControlledComponentExample;        

Un-Controlled Components

• In uncontrolled components, form data is handled by the DOM itself.
• The value of the form elements is managed by the DOM, and React does not control it directly.
• You can still access the form data using refs, but React doesn’t manage the state for these form elements.
• Uncontrolled components are useful when you need to integrate with non-React code or when you want to handle form data directly.

Example

import React, { useRef } from 'react';

function UncontrolledComponentExample() {
  const inputRef = useRef(null);

  const handleSubmit = (e) => {
    e.preventDefault();
    console.log('Input value:', inputRef.current.value);
  };

  return (
    <div>
      <form onSubmit={handleSubmit}>
        <input type="text" ref={inputRef} />
        <button type="submit">Submit</button>
      </form>
    </div>
  );
}

export default UncontrolledComponentExample;        

3. Difference between Redux Toolkit and Context API

Redux Toolkit

• State Management Approach: Redux Toolkit is built on top of Redux, which follows a centralized state management approach. It maintains the application state in a single store, allowing predictable state changes through actions and reducers.
• Global State Handling: Redux Toolkit is particularly suitable for managing global state that needs to be accessed and modified by multiple components across the application.
• Middleware Support: Redux Toolkit offers middleware support, enabling developers to intercept dispatched actions and perform asynchronous tasks like fetching data from APIs or logging actions.
• DevTools Integration: Redux Toolkit seamlessly integrates with Redux DevTools Extension, providing developers with powerful debugging capabilities to track state changes and action dispatches.
• Boilerplate Reduction: Redux Toolkit significantly reduces the boilerplate code associated with traditional Redux setups by providing utilities like createSlice for defining reducers, configureStore for setting up the store, and createAsyncThunk for handling asynchronous logic.

Example

// Redux Toolkit setup
import { configureStore, createSlice } from '@reduxjs/toolkit';

// Define a slice
const counterSlice = createSlice({
  name: 'counter',
  initialState: { value: 0 },
  reducers: {
    increment: state => {
      state.value += 1;
    },
    decrement: state => {
      state.value -= 1;
    },
  },
});

// Configure the Redux store
const store = configureStore({
  reducer: {
    counter: counterSlice.reducer,
  },
});

export const { increment, decrement } = counterSlice.actions;
export default store;        

Context API

• Component Tree Propagation: Context API is a part of React’s core library and facilitates the propagation of data through the component tree without explicitly passing props down at each level.
• Local State Management: Context API is more suitable for managing local state within a specific subtree of components rather than global state. It’s often used for simpler scenarios where sharing data between a few closely related components is required.
• Prop Drilling Avoidance: Context API helps in avoiding prop drilling by allowing components to consume context values directly from their nearest <Provider> ancestor.
• Simplicity and Flexibility: Context API is simpler to set up and use compared to Redux, making it a preferable choice for smaller applications or components where Redux might introduce unnecessary complexity.
• No Middleware Support: Unlike Redux Toolkit, Context API does not provide middleware support out of the box. As a result, handling asynchronous operations or side effects might require additional libraries or custom solutions.

Example

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

// Create a context
const CounterContext = createContext();

// Create a provider
export const CounterProvider = ({ children }) => {
  const [count, dispatch] = useReducer((state, action) => {
    switch (action.type) {
      case 'INCREMENT':
        return state + 1;
      case 'DECREMENT':
        return state - 1;
      default:
        return state;
    }
  }, 0);

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

// Custom hook to use the context
export const useCounter = () => useContext(CounterContext);        

Conclusion

Mastering the disparities between stateful and stateless components, controlled and uncontrolled components, and Redux Toolkit versus Context API is pivotal for ReactJS developers facing interviews. These distinctions reflect the nuanced approaches to state management, component behavior, and global versus local state handling. By grasping these differences, candidates can demonstrate their comprehension of fundamental ReactJS concepts, showcasing their ability to make informed architectural decisions and select appropriate tools for diverse project requirements.

Happy Coding!