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What is React.js and What is it Used for?

The variety of different tools that can be used for developing software can cause quite a headache. Ranging from front-end frameworks, through back-end, ending with libraries. The latter is what we’re gonna focus on in this article, particularly on answering the question: what is React?

By Wojciech Baranowski

Published: 23 August, 2021

Last update: 12 June, 2023

That being said, let’s dive into the article right now!

What is React?

In a nutshell, React is a JavaScript library created by Facebook. It’s the most popular library for building single-page applications and interactive user interfaces. Interestingly enough, oftentimes React is referred to as a framework.

Being open-source helps the library to stay on top of the popularity lists. According to a broad survey done by Stack Overflow, React.js has been the framework of choice for over 40% of people, with only jQuery beating it.

What’s a library though? On the contrary to frameworks, libraries are merely the means that you use for developing software. You’re not guided and not everything is served on a plate (like in the case of frameworks) but rather you’re the one who decides which tools to use and then you create a successful project.

We mentioned that React is a JavaScript library, but what exactly is JavaScript? Many of you most likely know the answer already, but for those unfamiliar with the term and technology, JavaScript is simply a scripting language used in web development. By using JavaScript, developers can program a wide range of dynamic content, graphics, animations, etc.

What is React Used for?

Being a JavaScript library, React is used in a lot of different projects. Why? Well, the answer is relatively simple – because it’s a really versatile tool. It can be used with different libraries and tools, such as Material UIRedux, or Create React App. Doing so can allow the library to spread the wings even more.

React can also be used as an additional library while building bigger projects with different frameworks. What’s more, it can also work with tools like React Router or React Navigation that are just a few examples of declarative components and navigation solutions that work magic with the library. Additionally, numerous resources are available, such as this React Native push notifications tutorial, which can guide you through the process of incorporating push notifications into your mobile applications for improved user interaction.

With React, developers can create dynamic single-page applications. Though, that wouldn’t be enough for React to succeed in the way it did. It had to feature something else – and it did, virtual DOM (Document Object Model) and JSX (JavaScript Syntax Extension).


Just like we mentioned in the previous paragraph, JSX is a syntax extension for the JavaScript language (sometimes also known as JavaScript XML) that uses simple, yet effective code similar to HTML. What’s more, the extension is a really versatile tool that allows the users to work with it on every platform with a browser.

Thanks to JSX, the code becomes more readable and it allows components to be stored in one file or catalog, which positively influences the reusability of the components. A little piece of trivia for you – if you find JSX familiar, you may have come across XHP, which is Facebook’s another extension syntax, but for PHP, not HTML.

What’s worth noting is that JSX is optional and isn’t required to run React.

Virtual DOM

Virtual DOM is a result of React manipulating the real DOM. Such action essentially creates a copy of DOM, hence the name – virtual DOM. Why is it used? Because it makes the library able to see which parts of the DOM need to be changed in order for the website to function properly and then it amends it.

What’s more, updating virtual DOM takes much less time than updating your regular Document Object Model, which makes React even more efficient.

But what is DOM actually? To put it plain and simple, DOM is an API structure that represents a document. In the case of DOM, either XML or HTML document.

Of course, there’s more to DOM than meets the eye, like usage of HTML attributes, but explaining the Document Object Model in detail would probably require a separate article.

How Did It Start?


In 2011 Facebook was already a well-established brand with its presence all around the world. Due to that fact, solutions that were used turned out to be outdated and simply weren’t enough anymore, that’s why Jordan Walke created a prototypical version of React, at that time known as FaxJS.

Two years have passed since the creation of React. In 2013, the library became open-sourced and has been officially released. This was a turning point in the history of React, as it marked its rapid expansion.

To this day, React gains popularity and as we mentioned before, is the most popular web development technology on the market.

Settling the Dispute: Framework or Library?

Let’s settle this once and for all. Is React one of JavaScript frameworks (as a lot of websites or charts suggest) or is it a library? Well, we did say it before – it’s definitely a library. But why is it called a framework when it’s a different thing? After all, it’s like calling a corn dog a hot dog.

Let’s go into detail with this question.

Similarly to many frameworks, React is designed to help developers build websites or web applications. That’s the reason why people still confuse React being a framework instead of a library.

A huge difference between a library and a framework is that frameworks already feature built-in tools that help developers create applications (which ironically may limit the framework in regards to picking additional third-party tools), but that’s not the case with React. When using React, you’d have to pick and choose the tools yourself.

It seems that choosing React over frameworks that already include various tools would be a bad idea. Not in the slightest! Developers who choose React and keep on practicing will eventually become skilled professionals with deep knowledge of other third-party packages and tools.

What’s more, React gives you a freedom that no framework could provide. You’re free to choose tools and packages with which you’d like to build your application.

To better understand the issue, let’s think about it in a different way. Imagine building model figures. A nice, beautiful set of model figures with different important and unique elements. Each component that we mentioned, is a part of a whole set, and that set represents a framework.

On the other hand, let’s visualize a jigsaw puzzle (representing a library), where you have to select and pick each puzzle separately to form a complete picture. See what I mean?

Even though React is similar to a framework, it beats almost every one of them in terms of popularity. After all these factors, we can safely say that React is a JavaScript library with features of a framework, ideal for web application development.

React Components

react components graphic

In simple terms, when you build an application using React, it’s made of small pieces of a puzzle, i.e. components. Thanks to them the developers can divide user interfaces into different bits. What’s a React component, though? Well, it’s essentially a JavaScript function that allows the library to receive inputs (also referred to as props). It then returns the elements that indicate what should be seen on the screen. What’s worth noting is that there’s also an instance called state that provides the developer with the ability to manage the internal status.

As you can see below, there’s more than one React component. Take a look.

Functional and Class Components

A couple of text lines above we mentioned props and these play a key factor in this React component. In functional components, the input is received which then returns JSX code. In other words, it displays information.

If you’d like to use lifecycle methods or state, you can do it with the help of so-called hooks. It essentially means that in class components you use React.Component class methods and manage state by using the setState method. In functional components, you can use the useEffect and useState hooks. Both components use different hooks but result in the same outcome.

Class components on the other hand, draw from React’s main functions that functional components don’t natively use, like state or lifecycle methods. Another difference can be seen in syntax.

Pure Components

Pure components are written in a similar fashion to class components, but they’re different. Their main task is to optimize the number of renders to provide the best outcome. What’s more, it’s the easiest React component out of all of them.

Higher-Order Components

React has a compositional nature and from that nature, a pattern arises. A pattern that’s called higher-order components. What they do is wrap a component. We know it may sound complicated but essentially they take one component and return a completely new one, in most cases with additional logic.

React Native

react native graphic

Did you think we were done? Not at all. When talking about React we have to mention React Native. As the name suggests, React Native is used for developing mobile applications.

React Native works based on JavaScript thread, contrary to the regular React library. JavaScript then reads the code and exchanges information with its components, resulting in compiling React components into native elements of the user interface.

With React Native a software engineer can even program mobile applications in Java or Swift (for Android and iOS respectively).

Why Should You Choose React?

Some of you may wonder, why should you choose React when there are so many other JavaScript frameworks like, for example, Ember or Angular? Let’s take a look at these few bullet points.

why you should choose react?

Easy and Simple to Learn

Even inexperienced developers can learn React as it’s quite easy to understand. Of course, developers with previous experience in other frameworks and programming languages would have much less trouble learning the library, but getting to know the basics of HTML, CSS, and JavaScript would go a long way for an aspiring developer to embark on the React journey.

Additionally, knowing how React works and how to integrate it with third-party tools would be a huge advantage.

#1 Choice Among Developers

Over 80,000 software developers have trusted React and let’s face it, the number will only keep on growing, as React tops the popularity charts time after time.

Large Community Support

A growing number of developers equals a growing number of supporters. With React being an open-source library, chances are that even if you get lost in the middle of a project or get confused while learning – the community will be there to provide all the necessary support.

Due to that fact, React will not fade away anytime soon. If you’re planning on building a project, it can be your go-to library.


React is one of the most versatile technologies available, as it can be used with a lot of different tools. What’s more, React can be applied only to certain parts of the project and it’ll still work like a charm!

Great Performance

React is a wonderful JavaScript library for building single-page applications, especially if you’d like to spend less development time while creating small apps.

Since React is a library, you can use it in cooperation with various tools and other libraries as well! As we mentioned before, it’s really versatile.

React in Everyday Life

Most of us use the web and mobile applications daily and let’s be honest, most likely more than once. But have you ever thought about how they’re made? Obviously, Facebook is one of the biggest companies that use React during development, but how about the others? Giants like NetflixDropBoxAmazonTeslaShopify, or Yahoo! Mails are only a few examples.

According to Stackshare, React is used by at least 9850 companies! That’s quite a score, don’t you think? What’s more, over 88,880 developers declared that they used or use React in their projects.

Key Takeaways

Distinguishing React between a framework and a library may cause some trouble. In order to avoid making any unnecessary mistakes, remember these points:

  • React is a library, not a framework;
  • It’s the most popular JavaScript library available;
  • React Native is meant to be used for developing mobile apps;
  • React is designed for building user interfaces, web applications, and more;
  • The library has a huge and supportive community;
  • Basic knowledge of HTML/CSS is enough to start learning React;
  • React development will keep gaining popularity;
  • The sky’s the limit!


And we’re almost done! Even though there are other JavaScript libraries like Vue.js, React is the undisputed king and that deserves recognition and respect.

We went through quite a lot of information, from explaining what React is, what it’s used for, through its beginnings, all the way to React Native and its use in different applications.

If you’ve never tried React and all of the above sounds appealing, make sure to check out the list of the best web development blogs that can help you learn React, different frameworks, and more!

Until next time!

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Wojciech Baranowski

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