React (JavaScript library)

React

Original author(s)	Jordan Walke
Developer(s)	Facebook, Instagram and community
Initial release	March 2013 (2013-03)
Stable release	15.5.4 / April 11, 2017 (2017-04-11)[1]
Repository	github.com/facebook/react
Development status	Active
Written in	JavaScript
Platform	Cross-platform
Size	145 KiB production 726 KiB development
Type	JavaScript library
License	3-Clause BSD with Facebook addendum (not OSI-approved)
Website	facebook.github.io/react

In computing, React (sometimes styled React.js or ReactJS) is an open-source JavaScript library^[2] for building user interfaces.

It is maintained by Facebook, Instagram and a community of individual developers and corporations.^[3][4][5]

React allows developers to create large web-applications that use data that can change over time, without reloading the page. It aims primarily to provide speed, simplicity and scalability. React processes only user interfaces in applications. This corresponds to View in the Model-View-Controller (MVC) template, and can be used in combination with other JavaScript libraries or frameworks in MVC, such as AngularJS.^[6]

History

React was created by Jordan Walke, a software engineer at Facebook. He was influenced by XHP, an HTML component framework for PHP.^[7] It was first deployed on Facebook's newsfeed in 2011 and later on Instagram.com in 2012.^[8] It was open-sourced at JSConf US in May 2013. React Native, which enables native Android, iOS, and UWP development with React, was announced at Facebook's React.js Conf in February 2015 and open-sourced in March 2015. On April 18, 2017, Facebook announced React Fiber, a new core algorithm of React framework library for building user interfaces.^[9] React Fiber will become the foundation of any future improvements and feature development of the React framework.^[10]

Notable features

One-way data flow

Properties, a set of immutable values, are passed to a component's renderer as properties in its HTML tag. A component cannot directly modify any properties passed to it, but can be passed callback functions that do modify values. This mechanism's promise is expressed as "properties flow down; actions flow up".

Virtual DOM

Another notable feature is the use of a "virtual Document Object Model", or "virtual DOM". React creates an in-memory data structure cache, computes the resulting differences, and then updates the browser's displayed DOM efficiently.^[11] This allows the programmer to write code as if the entire page is rendered on each change, while the React libraries only render sub components that actually change.

JSX

React components are typically written in JSX, a JavaScript extension syntax allowing quoting of HTML and using HTML tag syntax to render subcomponents.^[12] This is a React-specific grammar extension to JavaScript like the now-defunct E4X. HTML syntax is processed into JavaScript calls of the React framework. Developers may also write in pure JavaScript. JSX is similar to another extension syntax created by Facebook for PHP, XHP. JSX looks like regular HTML. An example of JSX code:

import React from 'react';

class App extends React.Component {
   render() {
      return (
         <div>
               <p>Header</p>
               <p>Content</p>
               <p>Footer</p>
         </div>
      );
   }
}

export default App;

Nested elements

Multiple elements need to be wrapped in a single container element like the <div> element shown above.

Attributes

Custom attributes are supported in addition to HTML attributes. The custom attributes need to be added with the data- prefix.

JavaScript expressions

JavaScript expressions can be used inside JSX with curly brackets {}:

import React from 'react';

class App extends React.Component {
   render() {
      return (
         <div>
            <h1>{10+1}</h1>
         </div>
      );
   }
}

export default App;

The example above will render "11".

Ternary operators

If–else statements cannot be used inside JSX but ternary expressions instead. In example below browser will render "true" because i is equal to 1.

import React from 'react';

class App extends React.Component {
   render() {
      var i = 1;
      return (
         <div>
            <h1>{ i === 1 ? 'true' : 'false' }</h1>
         </div>
      );
   }
}

export default App;

Architecture beyond HTML

The basic architecture of React applies beyond rendering HTML in the browser. For example, Facebook has dynamic charts that render to <canvas> tags,^[13] and Netflix and PayPal use isomorphic loading to render identical HTML on both the server and client.^[14][15]

React Native

React Native libraries were announced by Facebook in 2015,^[16] providing the React architecture to native Android, iOS, and UWP^[17] applications.

Future development

Project status can be tracked via the core team discussion forum.^[18] However major changes to React go through the Future of React repo, Issues and PR.^[19][20] This enables the React community to provide feedback on new potential features, experimental APIs and JavaScript syntax improvements.

Sub projects

The status of the React sub-projects used to be available in the project wiki.^[21]

Facebook CLA

Facebook requires contributors to React to sign the Facebook CLA.^[22][23]

Licensing

The initial public release of React in May 2013 used a standard Apache License 2.0. In October 2014, React 0.12.0 replaced this with a 3-clause BSD license and added a separate PATENTS text file that permits usage of any Facebook patents related to the software:^[24]

"The license granted hereunder will terminate, automatically and without notice, for anyone that makes any claim (including by filing any lawsuit, assertion or other action) alleging (a) direct, indirect, or contributory infringement or inducement to infringe any patent: (i) by Facebook or any of its subsidiaries or affiliates, whether or not such claim is related to the Software, (ii) by any party if such claim arises in whole or in part from any software, product or service of Facebook or any of its subsidiaries or affiliates, whether or not such claim is related to the Software, or (iii) by any party relating to the Software; or (b) that any right in any patent claim of Facebook is invalid or unenforceable."

This unconventional clause caused some controversy and debate in the React user community, because it could be interpreted to empower Facebook to revoke the license in many scenarios, for example, if Facebook sues the licensee prompting them to take "other action" by publishing the action on a blog or elsewhere. Many expressed concerns that Facebook could unfairly exploit the termination clause or that integrating React into a product might complicate a startup company's future acquisition.^[25]

Based on community feedback, Facebook updated the patent grant in April 2015 to be less ambiguous and more permissive:^[26]

"The license granted hereunder will terminate, automatically and without notice, if you (or any of your subsidiaries, corporate affiliates or agents) initiate directly or indirectly, or take a direct financial interest in, any Patent Assertion: (i) against Facebook or any of its subsidiaries or corporate affiliates, (ii) against any party if such Patent Assertion arises in whole or in part from any software, technology, product or service of Facebook or any of its subsidiaries or corporate affiliates, or (iii) against any party relating to the Software. [...] A "Patent Assertion" is any lawsuit or other action alleging direct, indirect, or contributory infringement or inducement to infringe any patent, including a cross-claim or counterclaim."^[27]

The Apache Software Foundation considers this licensing arrangement to be incompatible with its licensing policies, as it "passes along risk to downstream consumers of our software imbalanced in favor of the licensor, not the licensee, thereby violating our Apache legal policy of being a universal donor."^[28]

References

External links

• Official website