Basic usage
The following is a rudimentary example of using React for the web, written in JSX and JavaScript.Greeting
function is a React component that displays the famous introductory Notable features
Declarative
React adheres to theComponents
React code is made of entities called components. These components are reusable and must be formed in the SRC folder following the Pascal Case as its naming convention (capitalize camelCase). Components can be rendered to a particular element in the DOM using the React DOM library. When rendering a component, one can pass the values between components through "props":name
property with the value "Gulshan" has been passed from the Example
component to the Tool
component.
Also the return
section is wrapped in a tag because there is a limitation in the return
function, it can only return a single value. So all JSX elements and components are bound into a single tag.
The two primary ways of declaring components in React are through function components and class-based components.
Functional components
Function components are declared with a function that then returns some JSX. From React 16.8 version and above, Functional component can use state using Hooks.Higher Order Components
Higher order components (HOCs) are functions that take a component as an argument and return a new component. They can be used to add additional functionality to a component without modifying the original component. HOCs are a pattern that is often used in React to reuse code and abstract logic. For example, an HOC might be used to add error handling or data loading functionality to a component. One common use case for HOCs is to wrap a component with a higher-level component that provides additional functionality. For example, an HOC might be used to wrap a component with a component that adds a loading spinner while data is being fetched. HOCs can be a powerful tool for organizing and reusing code in a React application, and are often used to abstract complex logic or add additional functionality to multiple components.React hooks
On February 16, 2019, React 16.8 was released to the public. The release introduced React Hooks. Hooks are functions that let developers "hook into" React state and lifecycle features from function components. Hooks do not work inside classes — they let you use React without classes. React provides a few built-in hooks likeuseState
, useContext
, useReducer
, useMemo
and useEffect
. Others are documented in the Hooks API Reference. useState
and useEffect
, which are the most commonly used, are for controlling state and side effects respectively.
Rules of hooks
There are rules of hooks which describe the characteristic code pattern that hooks rely on. It is the modern way to handle state with React. # Hooks should only be called at the top level (not inside loops or if statements). # Hooks should only be called from React function components and custom hooks, not normal functions or class components. Although these rules can't be enforced at runtime, code analysis tools such as linters can be configured to detect many mistakes during development. The rules apply to both usage of hooks and the implementation of custom hooks, which may call other hooks.Class-based components
Class-based components are declared using ES6 classes.Virtual DOM
Another notable feature is the use of a virtualLifecycle methods
Lifecycle methods for class-based components use a form of hooking that allows the execution of code at set points during a component's lifetime. *ShouldComponentUpdate
allows the developer to prevent unnecessary re-rendering of a component by returning false if a render is not required.
* componentDidMount
is called once the component has "mounted" (the component has been created in the user interface, often by associating it with a DOM node). This is commonly used to trigger data loading from a remote source via an API.
*componentWillUnmount
is called immediately before the component is torn down or "unmounted". This is commonly used to clear resource-demanding dependencies to the component that will not simply be removed with the unmounting of the component (e.g., removing any setInterval()
instances that are related to the component, or an " eventListener" set on the "document" because of the presence of the component)
* render
is the most important lifecycle method and the only required one in any component. It is usually called every time the component's state is updated, which should be reflected in the user interface.
JSX
JSX, or JavaScript Syntax Extension, is an extension to the JavaScript language syntax. Similar in appearance to HTML, JSX provides a way to structure component rendering using syntax familiar to many developers. React components are typically written using JSX, although they do not have to be (components may also be written in pure JavaScript). JSX is similar to another extension syntax created by Facebook for PHP called XHP. An example of JSX code:Architecture beyond HTML
The basic architecture of React applies beyond rendering HTML in the browser. For example, Facebook has dynamic charts that render to
tags, and Netflix and PayPal use universal loading to render identical HTML on both the server and client.
Server-Side Rendering
Server-side rendering refers to the process of rendering a client-side JavaScript application on the server, rather than in the browser. This can improve the performance of your application, especially for users on slower connections or devices. With server-side rendering, the initial HTML that is sent to the client includes the fully rendered UI of your application. This allows the client's browser to display the UI immediately, rather than having to wait for the JavaScript to download and execute before rendering the UI. React supports server-side rendering, which allows you to render your React components on the server and send the resulting HTML to the client. This can be useful for improving the performance of your application, as well as for search engine optimization (SEO) purposes.Common idioms
React does not attempt to provide a complete "application library". It is designed specifically for building user interfaces and therefore does not include many of the tools some developers might consider necessary to build an application. This allows the choice of whichever libraries the developer prefers to accomplish tasks such as performing network access or local data storage. Common patterns of usage have emerged as the library matures.Unidirectional data flow
To support React's concept of unidirectional data flow (which might be contrasted with AngularJS's bidirectional flow), the Flux architecture was developed as an alternative to the popularUSER_FOLLOWED_ANOTHER_USER
. The stores, which can be thought of as models, can alter themselves in response to actions received from the dispatcher.
This pattern is sometimes expressed as "properties flow down, actions flow up". Many implementations of Flux have been created since its inception, perhaps the most well-known being Redux, which features a single store, often called a single source of truth.
Future development
Project status can be tracked via the core team discussion forum. However, major changes to React go through the Future of React repository issues and pull requests. This enables the React community to provide feedback on new potential features, experimental APIs and JavaScript syntax improvements.History
React was created by Jordan Walke, a software engineer atLicensing
The initial public release of React in May 2013 used the Apache License 2.0. In October 2014, React 0.12.0 replaced this with the 3-clause BSD license and added a separate PATENTS text file that permits usage of any Facebook patents related to the software: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. Based on community feedback, Facebook updated the patent grant in April 2015 to be less ambiguous and more permissive:
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.The Apache Software Foundation considered 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", and "are not a subset of those found in the pache License 2.0 and they cannot be sublicensed as pache License 2.0. In August 2017, Facebook dismissed the Apache Foundation's downstream concerns and refused to reconsider their license. The following month, WordPress decided to switch its Gutenberg and Calypso projects away from React. On September 23, 2017, Facebook announced that the following week, it would re-license Flow,
See also
* Angular (web framework) * Backbone.js *References
External links
* {{Authority control 2015 software Ajax (programming) Facebook software JavaScript libraries Software using the MIT license Web applications