React (React.js, ReactJS) is an open-source JavaScript library for creating composable user interfaces. It was built at Facebook and open-sourced in 2013. Now it is deployed in production at Facebook and Instagram is fully written in React. This library is not MVC (Model-View-Controller) framework, in fact it takes care only of “V” in MVC - rendering views. It was designed to create big applications featuring data that changes over time.
Unlike traditional UI building tools, React does not use HTML directives or templates. This library takes different approach: user interface is divided into components and subcomponents. Buttons, layout parts, form fields, etc. become reusable encapsulated components. This accelerates development process and reduces the number of bugs. React is great if you want an interactive UI. All you need to do is design states - how your application should look at any given point in time. With each change React will render and update only components related to this change. Code with such declarative views is much more easier to debug.
React features an optional syntax extension - JSX - for those who give preference to the HTML syntax readability over pure JavaScript. Library’s components are usually written in JSX, since it is easier, faster and safer than raw JavaScript. For example, while compiling the source code JSX catches many errors and performs optimization.
Also React provides specific approach to interaction with DOM. Traditionally, using JS applications you need to manually update DOM nodes to apply changes. React uses “fake” or “virtual” DOM. From outside it seems that API re-renders the whole application for each update. What really happens is that during initialization and data change of each component a lightweight in-memory data structure cache is created. When you need to perform an update, the differences in these caches are computed, based on which React library can generate a minimal set of changes that will be used by the DOM.
In short, React works with changes very effectively and performs the least amount of DOM manipulation by rendering only subcomponents (or subtrees of nodes) that were actually updated. Moreover, since React uses “virtual” DOM, you can run it not only on the client side, but also on the server and even make them work inter-operably. Rendering React server-side can improve performance, flexibility and SEO.
React can be used to write native iOS and Android apps using React Native framework. It was also developed by Facebook and is applied for its multiple production applications. This framework concentrates on quality, efficiency, and consistent look and feel across targeted platforms. It is reached via native platform components, powerful touch handling system, flexbox layout model, asynchronous execution of operations between the JavaScript app code and the native platform.
React is a simple, declarative, component-based JavaScript UI library. Its main aim is to provide views in the browser for data rendered as HTML. But React’s architecture can offer you much more than that. For instance, you can run React on the server, render dynamic charts to <canvas> instead of HTML, have consistent and standards-compliant event behaviour and event delegation, build "single page" web app using only React code like it was done by Instagram, create native apps with React Native, use isomorphic loading, etc. For more information visit React website and documentation.
If you are interested in creating state-of-the-art interactive UIs or improving already existing one, contact us and we will develop React-based solution for you.