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Guides How to Hire a Software Developer: The Ultimate Guide

How to Hire React JS Developers: Step by Step Manual

React JS is an open-source front-end JavaScript library for web and mobile development, often used with other libraries such as MobX, Redux, and GraphQL.

So far, based on the available StackOverflow and Stateofjs data, React JS is the most commonly used library for developing user interfaces.

In this article, we will analyze the key points you should consider when hiring React JS developers.

Content of the article:

React JS developer responsibilities

When you hire React JS developers, pay attention to their 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 React JS 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.

Every employer is primarily looking for talented professionals. For this purpose, they test and evaluate a professional’s skills – the hard skills. However, hard skills are not enough for project success. Employers also look at soft skills. Soft skills show how well a developer can interact with a team, manage it, or communicate with a client. 

 You can read more about the soft skills required for a software developer in our article Why Soft Skills Matter When Hiring a Software Developer.

React JS component libraries every mobile developer need to know

Another reason for React’s popularity is a large catalog of component libraries. When developers build applications, it’s the component libraries that save them time and effort. Pre-built components are buttons, menu items, forms, and more. By using pre-built components, the developer can perform the required functions in the application without having to create it from scratch. 

Below are the 8 most popular component libraries based on rating on Github:

  1. Ant Design – popular React UI library with many styled components ready for use.
    Github Stars: 73,700+
  2. Material UI – set of React components that implement Google’s Material Design specification.  
    Github Stars: 70,200+
  3. Chakra – provides a set of accessible, reusable, and composable React components that make it super easy to create websites and apps.
    Github Stars: 19,900+
  4. React Bootstrap – a front-end Stylesheet library.
    Github Stars: 19,800+
  5. Blueprint – React-based UI toolkit for the web.
    Github Stars: 18,000+
  6. Semantic UI React – UI component framework for theming websites.
    Github Stars: 12,400+
  7. Fluent – web represents a collection of utilities, React components, and web components for building web applications.
    Github Stars: 11,900+
  8. Evergreen – React UI Framework for building ambitious products on the web.
    Github Stars: 11,000+

These are just the most common component libraries. You may need more for your specific project.

Engage CTOs to formulate requirements for the developer.

For more information on why a CTO should be part of a team, read our article How to Hire a CTO for a Startup and Not to Fail.


How to interview React JS developers

When you hire React JS 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 – beginner level , middle – intermediate level, senior – high level.

5 Software Developer Levels: Whom to Choose
For more information about each developer level, what they do, and how to choose the right level, read our article.
5 Software Developer Levels: Whom to Choose

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.

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.

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.

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

Q2. Keys in React JS, 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.

Hire React JS Developers You Need
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Hire React JS Developers You Need
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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. To know more about the final step of the interview process, read our article Top 8 Best Coding Interview Platforms.


How much does it cost to hire React JS developers

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

You can read more about what affects the developer’s price in our article How Much Does It Cost to Hire an App Developer.

Where and how you can hire react js developers 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). To know more about models of cooperation, pros and cons, and resources on where to look for developers, read our article How and Where to Find Developers Who Meet Your Needs.

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