What is React.js and how can that technology be used to build a custom web application?

18 August 2021
Marcin Śpiewak
Marcin Śpiewak
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  • Intro

Anyone that is at least slightly interested in the web development world must have heard about React.js. It’s a powerful and popular front-end JavaScript library (not framework!). React is used to create many everyday use applications including Netflix, Facebook, Instagram, Airbnb, and Dropbox. 

What’s more, according to research by the State of JS, for a good couple of years it has held a strong position among other technologies in terms of developers’ satisfaction, awareness, interest, and usage.

And no wonder, since it lets entrepreneurs build custom web apps with beautiful interfaces and a remarkable User Experience. Compared to other technologies such as Angular.js, React brings excellent results when it comes to app performance and development speed (hence, development costs). 

With that in mind, let’s dive into the story that will answer your React-related questions, such as:

  • What is React.js?
  • What makes it stand out from other web development technologies?
  • What are the main benefits of React?
  • For what kind of projects will it be the best fit?

What is React.js?

The React library was created by Facebook developers in response to an issue that Facebook developers were facing. They were on the lookout for a way to build dynamic, interactive, and visually appealing interfaces with no loss in efficiency or performance. And that’s how React.js was born. 

Originally intended for internal projects, it was launched as open-source in 2013 and has taken the Javascript community by storm. It is still maintained by Facebook and now has millions of developers and hundreds of contributors. 

React.js is an efficient and elastic JavaScript library for building user interfaces. It allows engineers to quickly build complex UIs for web and mobile applications. Its approach to building a User Interface is component-based, meaning that a developer creates separate and isolated component pieces of code with their own properties and functions, making the whole code easier to debug.

This structure guarantees a number of business-friendly benefits. Here are a few of them:

  • better performance
  • faster development
  • lower maintenance costs
  • easier integration of new developers into projects (thanks to the clear code structure)

Except for the component structure, the uniqueness of React lies in two features – the usage of a JSX language and a Virtual DOM. Those who are interested in how it works will find a short, explanatory React.js Dictionary at the end of this article.

About the benefits of React.js

Vibrant open-source community

By choosing React.js, you get access to thousands of passionate React developers who keep contributing to its growth in the package. As one of the most popular open-source technologies, it has over 2M repositories on Github. However, React is now considered an established and stable technology. The community still creates new frameworks and tools, such as  Storybook and React Bootstrap. They also provide support for anyone who is new in the React world. Plus, it has the giant of Facebook standing beneath it.

It will save you time and money

There are thousands of reusable components available as open-source libraries. Developers can put them in various project slots, working more efficiently and not ‘reinventing the wheel’. This approach pushes much higher code quality while significantly decreasing the amount of time needed to build apps (therefore saving developers’ time and reducing project costs).

Better performance

React was created to solve the issue of lousy performance in the context of more complex applications. Long story short, it worked. Thanks to Virtual DOM, given its number of features and utility, it scores excellently when it comes to web performance, guaranteeing lightning-fast apps with low loading times.

Great UX and UI

React.js makes it easy to create dynamic web applications because it guarantees more functionalities with less coding, which is a direct benefit of its component structure. Virtual DOM offers a unique and effective way of updating an app’s views by only updating single components when changes are detected. This allows for the creation of advanced apps with interactive User Interfaces. The vast majority of components have been previously coded and placed in the Github repository.

One-way data flow

In React.js, how a user sees a component depends on its state. Any of their actions (such as clicking on a button or filling up a field) can change the component’s state. This change is transmitted to its view and, in sequence, to the inheriting components. 

This approach makes the application more efficient (as the relationship between particular elements of the interface is clearly defined), less prone to errors, and easier to debug (as a developer has greater control over the data flow). One-way data flow also makes it easy to analyze an app’s performance, since any slow-downs can be detected in the blink of an eye as the changes to a component affect only that component itself.


Crucial as it is, not many JavaScript frameworks deal well with search engine optimization. React.js drastically improves page load speeds, one of the primary criteria for the Google index algorithm. In addition, apps built with React are lightweight, offer server-side rendering, and can load in the blink of an eye. 

The benefits of React.js
The benefits of React.js

Cross-platform development with React Native

React Native is a framework created by Facebook to speed up the process of mobile app development. Previously written React code allows you to simultaneously build apps for both Android and iOS platforms. As it uses bridges to translate JavaScript into native components, code is used to build both iOS and Android native apps once it has been written.

This is perfect if you need to build an uncomplicated mobile app without many resources. The more complex the app’s features are, the more native code snippets need to be written. The code created for a web application may be reused for mobile ones – developers build a reusable library that can be leveraged in both web and mobile apps. 

Is it possible to create a server-side rendered app with React? 

First, we need to clarify the main differences between client-side rendering and server-side rendering.

In client-side rendering, a browser downloads a basic HTML web page then renders the JS parts and fills them with content. Server-side rendering means the React components are rendered directly on the server, delivering HTML content. 

Combining it into a web application that can be rendered on multiple platforms simultaneously, we get an isomorphic application that renders on both the server and the client (web browser) sides. Creating such an application, developers build one common component tree, which is rendered on a server after the request. This results in sending an HTML code with all the data to the browser, which later loads the JavaScript in the client version of a React application. 

There are two main advantages of such an approach:

  • improved SEO
  • better performance

Search engines don’t read JavaScript. If the content is not in HTML, they see it as a blank page, no matter how helpful it is. 

In server-side rendered applications, their performance depends only on the server’s resources and the capabilities of the users’ network. And it’s been said multiple times that improving the speed of an app improves the overall user experience drastically. 

When should you use React for web development?

React has proven its capabilities when building both Custom Web Applications (just take a look at Netflix, Instagram, PayPal, and many more) and simple single-page apps (SPAs). The main difference between a single-page application and a traditional multi-page app is that navigating a SPA does not require moving to an entirely new page. Instead, views load within the same page. When having a proper routing configured, single-page apps tend to be even faster and better optimized.

Getting back to the types of apps you can build with React.js… Well, there are a lot. 

Social Networks

Single Page App - Pinterest
Single Page App – Pinterest

Why does it work so well?

  • Great for building Single-Page Apps
  • Easy social sharing with server-side rendering
  • Simple real-time data processing with Websockets


  • Facebook
  • Instagram
  • Pinterest

Video Platforms

Video Platform - Netflix
Video Platform – Netflix

Why does it work so well?

  • Powerful single-page applications
  • Good performance


  • Netflix

Sharing economy platforms

Shared economy platform - AirBNB
Shared economy platform – AirBNB

Why does it work so well?

  • Great for building Single-Page Apps
  • Easy social sharing with the server-side rendering
  • Simple real-time data processing with Websockets


  • Uber
  • Uber Eats
  • Airbnb

SaaS platforms

SaaS platform - Invision
SaaS platform – Invision

Why does it work so well?

  • Component reusability
  • Quickly updated UI with Virtual DOM
  • Quick rendering of pages with isomorphic JS


  • InVision
  • Zapier
  • Asana

E-commerce platforms

Ecommerce platform - Shopify
Ecommerce platform – Shopify

Why does it work so well?

  • Easy component maintenance 
  • Great performance
  • Interactive SPAs


  • Shopify
  • Shopping.com

Communication platforms

Communication platform - Skype
Communication platform – Skype

Why does it work so well?

  • Great for building Single-Page Apps
  • Exquisite real-time data processing with Websockets


  • WhatsApp
  • Discord
  • Skype

What is a JSX language?

HTML files are the core of every basic website. They are read by web browsers and translated to appear on your devices as web pages with the desired UX and UI. To make it possible, browsers create a Document Object Model (DOM) – a structure of how the particular components are arranged on the website. 

Web developers may add dynamic content to the web pages by adjusting the DOM with programming languages like JavaScript and additional extensions. 

JSX (JavaScript eXtension) is a React extension for JavaScript that gives its users the opportunity to change the DOM with ready-to-use components written in simple HTML code. It is known to save them lots of time and significantly improve site performance. 

Virtual DOM in React.js

When not using JSX to modify the DOM, a website will probably go with HTML. And for basic, static websites, that is absolutely fine. However, things get tricky when you host a complex, dynamic website that requires lots of user interaction. In that case, the entire DOM has to reload every time a user clicks on a button or fills in some field(s) on a form.

In a scenario when a developer uses JSX to update the DOM of their website, React.js creates the Virtual DOM (VDOM). It’s a virtual image of a UI that is saved in the memory and synchronized with the real DOM by a library (such as ReactDOM). Using React’s declarative API, you can notify the DOM about which components need to be selectively refreshed and which ones should stay the same. This way, the page load speed improves, computer and internet memory usage decreases, and this results in a faster, more user-friendly site. 

Wrapping up

React.js is a powerful JS library that brings many benefits such as component reusability, Virtual DOM, performance, and stability, unidirectional data flow, and many others. Although it is not the perfect solution for any case, it has helped many great businesses like Skype, Instagram, and Shopify to achieve their successes.

It’s up to you to decide which technologies will take part in your own success – we hope this article has imparted some wisdom to you. Feel free to contact us if you have any doubts about React or picking the right technology stack for your project!

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