13 React.js Developer interview questions and answers

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Describe the major features of React Native? 

A great way to determine your programmer's depth of knowledge is to explain some features of this coding language. Look for answers with the following included:

  1. React uses the virtual DOM instead of the real DOM element
  2. React uses server-side rendering
  3. React follows data binding or a unidirectional data flow 
  4. React uses specific lifecycle methods

Why can't browsers read JavaScript XML JSX?

A programmer should understand how browsers read JavaScript objects, and they should know how to enable them to read XML JSX. In addition, familiarity with JSX transformers like Babel indicates that they know how to change these java objects to pass them into the browser.

What is considered an event in React?

There are many basic triggered reactions within the react application. A qualified contractor should identify these events, such as a mouse hover or onclick press, and describe event functionality through its event handler. Knowing why events react and tracing back their syntax to the event handler is crucial for writing and executing react code.

Why do you use useState in React?

Your qualified freelancer should understand the functionality of the useState hook and how it allows state variables within a functional component. Understanding useState indicates that the coder knows how to create functional higher-order components without switching to class components. This method should typically be performed using the built-in setState() constructor method.

What are the differences between controlled and uncontrolled components?

Since every app has more than one form, knowing how to handle the form state of components is key. Your programmer should clearly distinguish between controlled, which is handled by a react component, and uncontrolled input value, handled by the DOM element itself.

Why are Pure components in React useful?

An experienced developer should already be using .PureComponent as a significant way to optimize the react app. This component provides a considerable performance increase because it reduces the number of render operations within the application. Knowing how to use this component shows they understand optimization. They can also use it to identify extra re-rendering to perform debugging and trigger alerts if the front-end or native element components need updating. 

Why is the default value of React.Component important?

The default initial state of a React.Component always has the value of shouldComponentUpdate set to return "true." Your programmer needs to understand this process of setting default values for props arguments—understanding how default values are set and why they are essential for passing prop properties and component classes. 

What is the process for updating a rendered element in React?

Rendered objects are often updated within React, so your experienced programmer should have this skill. Ideally, your developer should mention that since react elements are not mutable, once you create your elements, you cannot change its parent component, child component, current state, or current value attributes. Furthermore, since you cannot reuse elements, you must create new elements, and the only way is to pass it through ReactDOM.render().

What is the react-router?

A react-router is client-side routing, which allows you to build single-page web applications and navigation without refreshing the page algorithm as a user navigates. These routers can be used for both Android or IOS functionality. While your qualified developer should know what this router does, it's more important that they understand when to and when not to use a react-router. Often, the react-router can be an overkill for specific projects, so ask your programmer why and when they would use the react-router. 

Write a piece of code to render a button:

Rendering a button is one of the most basic React coding exercises. Have your programmer go through a few simple codes and see how they work through the specific syntax. 


import React from "react";

import ReactDOM from "react-dom";

import "./styles.css";

function Button(props) {

return (

<button type="submit">{props.label}</button>



const rootElement = document.getElementById("root");

ReactDOM.render(<Button label="Save" />, rootElement);


What is Redux?

Redux is an open-source JavaScript library with javascript functions that are used to manage the application state. Ask your developer why they would use Redux for their apps, and their answer should include some of the following:

  • The app has large amounts of application states that are needed in many places in the app
  • It is a great ecosystem for the application's state management
  • The app state is updated frequently.
  • The logic to update that state may be complex
  • The app is worked by many people

Why would you use a componentDidUpdate?

Your programmer should know when and when not to use this componentDidUpdate() feature. For example, it is useful when the DOM is updated, and the queue is empty, and your programmer should know the order in which this update should be executed. In addition, knowing how to use this component indicates your programmer is familiar with complex renders and state or DOM changes.

What is Flux?

Flux is the architecture that Facebook uses when working with React. Your programmer should be able to make the distinction that Flux is not a framework or a library. It is just a new kind of architecture that complements React with a concept that enforces a unidirectional data flow, provides stability to the application, and is a run-time error reducer. 



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    Wajahat S.
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    • 4.9
    • (49 jobs)
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    AI Speech-to-Text
    MERN Stack
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    Hi! My name is Shaw and I am a Full Stack Mobile (ReactNative) and Web (ReactJS NodeJS) Developer. I have worked as an Android and React Native Mobile Developer to build the mobile native and cross platform scalable apps. In addition to this I have the expertise of working on React as a front-end framework and Node on the server side using the Express Server for the seamless web experiences. I have a skilled and experienced commercial background and have been involved in providing solutions for mobile apps and design with state of the art technology. Following the latest trends and practices is one of my key attribute. Your work is my responsibility with flexible working hours according to your demand and wide window of communication and adjustability. Client's satisfaction is my first priority. I at programming not only build, I innovate. Come let's shake hands and build the future.
  • $35 hourly
    Karthick N.
    React.js Developer
    • 4.9
    • (18 jobs)
    Namakkal, TN
    vsuc_fltilesrefresh_TrophyIcon React.js
    Website Content
    Internet of Things Solutions Design
    Ruby on Rails
    Artificial Intelligence
    Machine Learning
    Computer Vision
    Deep Learning
    I've studied computer science. I have an experience of Web Development with the flavor of HTML, CSS, Bootstrap, JavaScript and other web development tools. I really enjoy the fact that thousands of users use applications that are developed by me. The ultimate dream is that one day thousands will grow into millions or billions. I HAVE A DREAM! Overall if summarized my experience that would be exploring, organizing information, problem-solving, and implementation. Languages are essential for expressing your programming skills overall. From the EXPLORING attribute, I have worked around lots of different languages. 1) Ruby 2) AngularJS 3) Javascript 4) Vuejs 5) Python ( a new sensation I always wanted to explore Erlang but then I found this beauty. Python leverages the Erlang VM, known for running low-latency, distributed and fault-tolerant systems, while also being successfully used in web development and the embedded software domain.) In assistance to above languages below frameworks come into play, 1) Ruby on Rails 2) Django Databases are the main central storage of any web application. I got experience in both SQL and NoSQL 1) Postgres 2) MongoDB 3) SQLite 4) Mysql The game never ended on the server-side for me. The frontend/public-facing part of the web application has been also highly evolved. Everyone wants to use Single Page Applications - The SPAs. I got experience in the following 1) Angular JS 2) React JS Testing and Test Driven Development(TDD) is also an essential thing for any solid application. I can write automated tests in following 1) Rspec 2) Capybara Deployment is essential to distribute your application out in the wild. I got experience in the following tools and technologies 1) AWS 2) Google Cloud Platforms 3) Capistrano 4) Mina 5) Nginx 6) Passenger Phusion 7) Puma 7) Unicorn
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    Kimera M.
    React.js Developer
    • 5.0
    • (4 jobs)
    Kampala Central Division, C
    vsuc_fltilesrefresh_TrophyIcon React.js
    Tailwind CSS
    React Bootstrap
    RESTful API
    Material Design
    CSS 3
    Adobe XD
    Hi Thanks for stopping by👋 Online presence of any business is a major attribute to it's success. Every business should always make it's brand known to the general public which can easily translate into revenue. Do your needs fit into any of these questions listed below? Send me a message and we discuss about your project. 🤔Do you have an XD/Figma designs that you want to translate into reusable code using HTML, CSS, JavaScript or React Js? 🤔 Do you want a website for any business but you don't know where to start from? 🤔 Is your website not responsive enough to be used on all platforms and you want it made responsive? 🤔 Want to add a particular functionality to your website? 🤔Want to create a more engaging user experience from your brand than just displaying content on static web pages? 🤔Finding it hard as to come up with a "compelling" and a "engaging" designs and flow for your brand? 🤔 Have any API you want integrated to your designs? Name it.., I'm here to help you with anything regarding web design and development from design to trouble shooting all the errors aligned with your website to personalization of your website content and design with in a short period of time . With my expertise and knowledge, I got you covered with everything to do with web designing and development. For the past4 years, I've been building web applications for all people from individuals to businesses owners who are interested in all sorts of functionalities like E-commerce, business profiles, custom systems with custom functionalities, Custom dashboards among others. I have a very efficient workflow and process while doing all this. I have expertise in developing beautiful, professional, reliable and affordable websites I'm proficient in the following: 🌟 Languages: ✔️ HTML ✔️CSS ✔️ JavaScript ✔️ Sass ✔️ NodeJS 🌟 Frame Works ✔️ React Js ✔️ Express Js 🌟 CSS Options ✔️ Tailwind CSS ✔️ Bootstrap ✔️ Material UI ✔️ Chakra UI ✔️ Styled Components ✔️ CSS modules 🌟 Design Tools ✔️ Figma ✔️ Adobe XD 🌟Version Control ✔️ Git ✔️ GitHub ✔️ GitLab 🌟 Other Technologies ✔️ Redux ✔️ React Router ✔️ Postman ✔️ Heroku ✔️ MongoDB Here's what to expect while working with me👇: ✔️ Pixel Perfect website designs and layout. ✔️ Fully responsive websites for both Mobile and Desktop Devices. ✔️ Fully Compatible websites with all browsers like Chrome, Firefox, Microsoft Edge, etc. ✔️ Clean, editable, reusable and tested code that can be changed from time to time. ✔️ Fully tested and finished web designs and code on real devices. ✔️ Expert help on trouble shooting errors aligned with website layouts in any browser. ✔️ Quick turn around and meeting deadlines no matter the size of the project. ✔️ Effective Communication and Attention to detail on every little aspect. ✔️ Fulltime Availability. Look at some of my work in relation to web design and development as listed in the projects section. When you hire me👨‍💼, here's what we would do: 1: First, click the invite button to invite me to your job📩 2: Once there, I'll jump on a phone call with you/video call📞 or exchange ideas with you about your needs. 3: We'll go over the details, colors🎨, assets, and the entire design/look of the template, design etc., until we have reached a middle ground So, if that sounds good, click the "invite" button, and we can start right away. Take a look at my website for more information kimeramoses.com Thanks for taking time to view my profile 🤝. Cheers🙋‍♂️, Moses.
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