Vaibhav Kumar

Posted on May 6 • Updated on May 14

Top 20 ReactJS interview questions to get a job

#webdev #react #reactjsdevelopment #interview

Calling all ReactJS rockstars and blog-lovin' bookworms! I'm your friendly neighborhood code-slinging wordsmith with a serious case of "never enough to say."

The trouble is, sometimes my brain explodes with awesome ideas, but my fingers just can't keep up. Enter the plot twist that's cooler than my latest CSS animation: AI! Yep, that's right, we're about to mash up human creativity with a sprinkle of artificial intelligence to create the most epic ReactJS interview question smackdown this side of the internet.

No robots were harmed in the making (just a few lines of code), but there's a whole lot of fun and killer content on the way! So, buckle up, buttercup, because we're about to show you what happens when a blogger with a keyboard and a super-powered AI join forces. Let me know in the comments if you dig this AI-powered blog idea, and get ready for a wild ride!

Just a few days ago, I totally aced an interview at a cool startup. Feeling like a ReactJS rockstar, I realized it was high time to dust off my blogging keyboard. Let's face it, my writing muscles were getting flabby from all that code flexing.

So, here's the plan: we're diving headfirst into the world of ReactJS interview questions. Not only will this help you slay your next interview, but it'll also get my blogging mojo flowing again (gotta keep those writing skills sharp, right?).

Okay, enough talking let's dive into the questions and answers!!

What is ReactJS?

ReactJS is a JavaScript library developed by Facebook for building user interfaces, particularly for single-page applications. It allows developers to create reusable UI components that efficiently update and render data changes.

What are the key features of ReactJS?

ReactJS boasts several key features including:

Virtual DOM for efficient rendering.
JSX syntax for writing component structures.
Component-based architecture for code reusability.
Unidirectional data flow via props and state.
Lifecycle methods for managing component behavior.

Explain JSX and its benefits.

JSX (JavaScript XML) is a syntax extension for JavaScript that allows developers to write HTML-like code within JavaScript files. Its benefits include:

Familiarity for developers accustomed to HTML.
Enhanced code readability and maintainability.
Compile-time error checking for syntax errors.
Improved performance through JSX's optimization capabilities.

What is the Virtual DOM in ReactJS?

The Virtual DOM is a lightweight, in-memory representation of the actual DOM. ReactJS uses the Virtual DOM to efficiently update and render UI components by minimizing direct manipulation of the browser's DOM. Changes are first applied to the Virtual DOM, and then React determines the most efficient way to update the actual DOM, resulting in improved performance.

What are props in ReactJS?

Props (short for properties) are a mechanism for passing data from parent to child components in React. They are immutable and are used to customize and configure child components based on the requirements of the parent component.

What is a state in ReactJS?

The state represents the internal data of a component that can change over time due to user interactions or other factors. Unlike props, the state is managed within the component itself and can be updated using the setState() method. Changes to the state trigger the re-rendering of the component and its child components.

import { useState } from "react";

export default function ExampleState() {

const [state, setState] = useState(0)

return (
<div>
    {state}
</div>
)};

Differentiate between props and state.

Props are immutable and passed from parent to child components, while the state is mutable and managed within a component. Props are used for configuring child components, whereas the state is used for managing component-specific data and triggering re-renders.

Explain the significance of keys in React lists.

Keys are special attributes used to identify unique elements in a React list. They help React identify which items have changed, been added, or been removed, enabling efficient updates and reordering of list items without re-rendering the entire list.

What is the purpose of the setState() method?

The setState() method is used to update the state of a component. It takes an object containing the updated state properties as an argument and triggers a re-render of the component and its child components with the new state values.

How can you handle events in ReactJS?

In ReactJS, events are handled using synthetic event wrappers provided by React. Event handlers are defined as methods within components and are passed as props to the corresponding DOM elements. Common event handlers include onClick, onChange, onSubmit, etc.

Explain the concept of lifting the state up in React.

Lifting state up refers to the practice of moving the state from child components to their nearest common ancestor in the component hierarchy. This allows multiple components to share the same state, enabling data synchronization and communication between sibling components.

What are the controlled components in ReactJS?

Controlled components are form elements whose values are controlled by the React state. They receive their current value and onChange event handlers as props, allowing React to maintain full control over the input values and synchronize them with the component's state.

Explain React context and its use cases.

React Context is a feature that allows you to share data across the component tree without having to pass props manually at every level. It provides a way to pass data through the component tree without having to use props drilling (passing props down through each level of the component hierarchy).

Use Cases of React Context:

Global Data Sharing: React context is particularly useful for sharing global data such as user authentication status, theme preferences, localization settings, etc., across multiple components.
Theme Switching: Imagine you have a theme switcher component that allows users to toggle between light and dark themes. Using context, you can share the current theme throughout your application without explicitly passing it to each component.
User Authentication: When handling user authentication, you might need to access the user's authentication status from various components. Context can help you share this information globally across your application.

What are hooks in React?

Hooks are functions that allow functional components to use state and other React features without writing a class. They were introduced in React 16.8 and include useState for managing state, useEffect for handling side effects, useContext for accessing context, and more.

What is the purpose of the useEffect() hook?

The useEffect() hook is used to perform side effects in functional components. It replaces lifecycle methods like componentDidMount, componentDidUpdate, and componentWillUnmount in class components and allows developers to manage side effects in a declarative and composable manner.

Explain code splitting in React and its benefits.

Code splitting is a technique used to split a React application's bundle into smaller chunks that are loaded asynchronously. This can significantly reduce the initial load time of the application, improve performance, and enhance the user experience, especially on slower network connections.

What are the advantages of server-side rendering (SSR) in React?

Server-side rendering involves rendering React components on the server and sending the generated HTML to the client, as opposed to rendering them in the browser. SSR offers benefits such as improved SEO, faster time to content, better performance on low-powered devices, and enhanced perceived load times for users.

Now let's add some coding interview questions also

Create a React component that fetches data from an API and displays it in a list.

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

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

  useEffect(() => {
    const fetchData = async () => {
      try {
        const response = await fetch('https://api.example.com/data');
        const jsonData = await response.json();
        setData(jsonData);
      } catch (error) {
        console.error('Error fetching data:', error);
      }
    };

    fetchData();
  }, []);

  return (
    <div>
      <h2>Data List</h2>
      <ul>
        {data.map(item => (
          <li key={item.id}>{item.name}</li>
        ))}
      </ul>
    </div>
  );
};

export default DataList;

Implement a controlled input component that updates its value based on user input.

import React, { useState } from 'react';

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

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

  return (
    <div>
      <label>Enter something:</label>
      <input type="text" value={value} onChange={handleChange} />
      <p>You entered: {value}</p>
    </div>
  );
};

export default InputComponent;

Create a React component that renders a list of items and allows the user to delete items from the list.

import React, { useState } from 'react';

const ItemList = () => {
  const [items, setItems] = useState(['Item 1', 'Item 2', 'Item 3']);

  const handleDelete = index => {
    const updatedItems = [...items];
    updatedItems.splice(index, 1);
    setItems(updatedItems);
  };

  return (
    <div>
      <h2>Item List</h2>
      <ul>
        {items.map((item, index) => (
          <li key={index}>
            {item}
            <button onClick={() => handleDelete(index)}>Delete</button>
          </li>
        ))}
      </ul>
    </div>
  );
};

export default ItemList;

BONUS QUESTION 😁:

Create a React component that displays a countdown timer. The timer should start at a specified duration and count down to zero.

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

const CountdownTimer = ({ initialDuration }) => {
  const [duration, setDuration] = useState(initialDuration);

  useEffect(() => {
    const timerId = setInterval(() => {
      setDuration(prevDuration => {
        if (prevDuration === 0) {
          clearInterval(timerId);
          return 0;
        } else {
          return prevDuration - 1;
        }
      });
    }, 1000);

    return () => clearInterval(timerId);
  }, [initialDuration]);

  const formatTime = time => {
    const minutes = Math.floor(time / 60);
    const seconds = time % 60;
    return `${minutes}:${seconds < 10 ? '0' + seconds : seconds}`;
  };

  return <div>Time remaining: {formatTime(duration)}</div>;
};

export default CountdownTimer;

Alright, that's a wrap on this ReactJS interview question rodeo! Big thanks to AI for being my super-powered writing partner – we make a pretty awesome team!

Now, the real question is: did this blog post help you on your ReactJS journey? Hit me with a comment below and let me know! Your feedback fuels my blogging fire, and any interview woes you have are fair game too.

Remember, the comment section is your oyster. Questions, confessions, interview horror stories – unleash them all! Until next time, keep on coding, keep on learning, and keep on rocking those ReactJS skills. See you around!