React Interview

React JS Developer Responsibilities

When you hire a React developer, pay attention to his responsibilities.

He may perform the entire list of these responsibilities or only a portion of them:

1. Collaborating with developers and designers to build web apps

2. Developing reusable and future-proof components

3. Website layout

4. DOM rendering

5. Designing a scalable app architecture and the APIs to support it moving forward

Skills Required For a React JS Developer

The skills required may vary from case to case, and experience in a particular field may be required. However, we’ve compiled a list of the most important skills to look for if you decided to hire ReactJS developers.

**Hard Skills to Look for in a React **

1. Good knowledge of CSS, HTML, as well as CSS frameworks such as-Bootstrap, and CSS preprocessor-LESS/ SCSS

2. Good knowledge of JS, JS ES6, TypeScript

3. Knowledge of Webpack/Browserify tools

4. Experience using Git as a management system

5. Experience with React Router library

6. Understanding the principles and concepts of React JS: Virtual DOM and JSX.

7. Experience with Flux and Redux architectures

8. Knowledge of ways to send data over HTTP – Rest/GraphQL

9. Knowledge of at least one testing framework – Jest, Enzyme, Cypress, Selenium

10. Experience with Type checkers such as Flow and ProTypes

**Universal Soft Skills to Look for in a React Developer **

1. Communication

2. Teamwork

3. Prioritization

4. Flexibility

5. Creativity

6. Proactivity

Junior vs. Middle vs. Senior React JS Developer: Whom Do I Need

When you hire ReactJS developers, you’ll probably wonder what level of developer you need for your project. The higher a developer’s level, the higher their salary.

Developers are divided into three gradations based on their skills:

**Junior. **This developer performs the simplest tasks assigned to him by his middle and senior colleagues. He is usually assigned to a project where there is already a senior with the same tech stack to save the senior’s time by transferring standard and routine tasks to the junior. So, he can gradually bring the developer up to the necessary level. There is no question of autonomy here.

**Middle. **This developer can perform tasks at a higher level. Independence is emerging, but the outcome of his work has yet to be reviewed by the lead developer on the project.

**Senior. **This developer can solve problems of any complexity. He can manage the project, decompose tasks and perform them independently. The required level of control is minimal. You set a goal – he gives you a solution.

How to Interview ReactJS Developers

So, you have decided what level of React JS Developer you need. Now, let’s discuss how to test the skills for each specific case.

Junior React js Interview Questions

Ask what technologies the developer has. Ask questions about the CSS language and CSS extensions.

What does it take to be a junior developer?

Q1. Does React use HTML?

A1. React uses a programming language called JSX, which is similar to HTML.

Q2. What is the CSS box model? How to change the position of boxes on a browser page?

A2. The CSS box model describes the rectangular boxes generated for elements in the document tree and created according to the visual formatting model. You can change the position of the boxes using position, margin, and transform.

Q3. How do you give components a name in React?

A3. If you want the component to be visible, start with a capital letter. With a lowercase letter, React processes the components as DOM tags.

Q4. What happens when you call setState?

A4. setState() schedule changes to the component’s state object and tells React this component, and its children need to be re-rendered with the updated state.

Middle React js Interview Questions

If the developer answers the general questions well, you can move on to the next part and ask questions exclusively about JS. The way the developer answers questions about JS will give you a complete picture of his capabilities. This happens because React, as mentioned earlier, is built on JS. And if React can be mastered in a month or two, it will take much longer for the developer to master JS well.

Jay.devs have the best dedicated resources for your project

Q1. What is the name of transforming JSX to JS?

A1. Transpilation. Transpilers take the source code and convert it into another language. Transpile JSX to JS is performed using Babel/TypeScript. Packages of all the modules in your application into one or more bundles are done via Webpack.

Q2. What does null mean in Javascript? What is the difference between undefined and null?

A2. Null assumes no object value (variable). Often used as an empty reference where an object is expected. For example, if an object reference is no longer needed (object=null), then the object reference is deleted.

The difference between null and undefined is that null – the absence of value for a variable, and undefined – the absence of a variable itself.

Q3. Does JS support multiple inheritances?

A3. No. Every object in JS has a single associated prototype. JavaScript cannot dynamically inherit from more than one prototype chain.

Q4. What is an Event loop in JS?

A4. Event Loop is an infinite cycle that waits for tasks, executes them, and waits for new tasks.

The event loop is a constantly running process that monitors both the callback queue and the call stack. If the call stack is not empty, the event loop waits until it is empty and places the next function from the callback queue to the call stack.

Senior React js Interview Questions

To hire a senior-level developer, you should ask questions without a straight answer. Then you can understand how well the developer is immersed in the subject and how deep his experience is.

Senior react js developer: “I found a bug”

Q1. How to use setTimeout/setInterval in a React function component?

Q2. Keys in Reactjs, why are they needed, on what principle should their value be set, what happens to the component when the key value changes?

Q3. There is a project that has performance drop on a certain event (for example, by clicking a button), you need to discover what the problem is as soon as possible, what can be done to find out what the problem is (here senior developer should name at least 2 tools)

Q4. setTimeout(function cb() {

console.log(‘1’);

}, 0);

console.log(‘2’);

Why is 2 and then 1 output at the beginning of the console (setTimeout is set to 0 ms)? In what case is 1 output after 2 in the console? Give an example of code that can be written below the current one (the current one cannot be changed) that delays the output of 1 for 1 second. What happens on the website when such code drops into a real project?

We need to clarify that we are intentionally not answering questions for the senior specialist. The reason is that usually, questions and answers for junior and middle developers can be found on the internet, and the applying developer can use them. Therefore, use the junior and middle React JS developer questions given here with caution and only as an example.

Our Solution Architect compiled the senior developer questions, and you won’t find the answers to them on the internet. We use them to interview our developers, so you need to understand why we don’t want to show the answers.

If you are looking for a senior React JS developer, you can contact our company, and we will be happy to help you find the right specialist. Or we can give you answers to the above questions, but only in a personal way.

Coding Challenge

The final step in choosing a suitable React JS developer is the so-called Coding Challenge. It is a practical task to test the developer’s skills.

We will list 3 main sites from which you can take tasks to check the developer:

1. Coderbyte. Good for finding logical, mathematical, algorithmicе tasks for interviews.

2. HackerEarth. Offers practical tasks and technical coding tests.

3. CodeSignal. The platform sends coding tasks that developers may encounter in real work.

Don’t make the mistake of thinking that practical skills are more important than theory or vice versa. They should complement each other.

Where To Find ReactJS Developers For Hire

So, you know what responsibilities a React.js developer has, what skills he or she needs, and how to interview a React.js developer.

It’s now time to find out where you can hire ReactJS developers.

Where and how you can hire a developer depends on the form of cooperation. This depends on the specifics of your project.

Generally, you have three options: in-house, freelance, or dedicated developers (on-demand developers).

In-house Developer

Here, you hire an employee directly into your workforce.

This is usually done when the position is key, and enough candidates have the required skills in the local job market. The advantage of this approach is you can “grow” your employees from junior to senior. However, there are also disadvantages: higher costs due to rates, taxes and office maintenance, and a limited choice of candidates.

Where: websites with vacancies (e.g., indeed), social networks (ex. LinkedIn), a recruitment agency.

Freelance Developer

An independent contractor who usually works under a contract. Often, such performers are hired for short-term projects or small, irregular tasks when there is no person with the required skills in the company. However, sometimes, it becomes difficult to control such a performer.

Where: Freelancer exchanges (e.g., Upwork), social networks (e.g., Facebook groups), recommendations from friends.

Dedicated Developer

A specialized IT company employs this person, and who is mainly helping you full-time with the development of your project. You pay the IT company for having their employee work for you. This model can be useful if you are limited to your local labor market or want to reduce the cost of a developer’s salary while maintaining maximum control over their work.

Where: B2B platforms (ex. Clutch), IT companies providing dedicated developers (ex. JayDevs)

How Much Does It Cost To Hire ReactJS Developers

It’s also worth noting what costs you should expect to pay if you want to hire reactjs developers.

Based on Neuvoo, Glassdoor, and Salaryexplorer, we’ve compiled rounded, comparative annual React JS developer salary data (by region and developer level):

React JS developer salary by region and developer level

The price of a developer can be affected by the following factors:

1. location of the developer

2. collaboration model

3. experience of the developer