What is react?
The react npm package is a JavaScript library for building user interfaces, particularly for single-page applications. It allows developers to create reusable UI components and manage the state of their applications efficiently.
What are react's main functionalities?
Component-Based Architecture
React allows developers to encapsulate UI logic and design into components, which can then be composed to build complex user interfaces.
class Welcome extends React.Component {
render() {
return <h1>Hello, {this.props.name}</h1>;
}
}
ReactDOM.render(<Welcome name='Jane' />, document.getElementById('root'));
State Management
React provides a way to manage the state within components, enabling dynamic and interactive user interfaces.
class Counter extends React.Component {
constructor(props) {
super(props);
this.state = { count: 0 };
}
increment = () => {
this.setState({ count: this.state.count + 1 });
};
render() {
return (
<div>
<p>{this.state.count}</p>
<button onClick={this.increment}>Increment</button>
</div>
);
}
}
Lifecycle Methods
React components come with lifecycle methods that are invoked at specific points in a component's lifecycle, allowing developers to hook into the component's creation, updating, and destruction processes.
class Timer extends React.Component {
componentDidMount() {
this.timerID = setInterval(() => this.tick(), 1000);
}
componentWillUnmount() {
clearInterval(this.timerID);
}
tick() {
this.setState({
date: new Date()
});
}
render() {
return (
<div>
<h2>It is {this.state.date.toLocaleTimeString()}.</h2>
</div>
);
}
}
Hooks
Hooks are functions that let developers 'hook into' React state and lifecycle features from function components. They provide a way to use stateful logic without writing a class.
import { useState, useEffect } from 'react';
function Example() {
const [count, setCount] = useState(0);
useEffect(() => {
document.title = `You clicked ${count} times`;
});
return (
<div>
<p>You clicked {count} times</p>
<button onClick={() => setCount(count + 1)}>
Click me
</button>
</div>
);
}
Other packages similar to react
vue
Vue.js is a progressive JavaScript framework used for building user interfaces. Unlike React, which is only the view layer, Vue includes a more comprehensive set of tools for building web applications, including a routing solution and state management solution.
angular
Angular is a platform and framework for building single-page client applications using HTML and TypeScript. Angular is more prescriptive than React, providing a standard way to structure an application and including a wide array of features out-of-the-box, such as dependency injection, templating, routing, and more.
preact
Preact is a fast, 3kB alternative to React with the same modern API. It provides the thinnest possible Virtual DOM abstraction on top of the DOM. Preact is a good choice for when performance is critical, and the application needs to be as lightweight as possible.
svelte
Svelte is a radical new approach to building user interfaces. Whereas traditional frameworks like React and Vue do the bulk of their work in the browser, Svelte shifts that work into a compile step that happens when you build your app, resulting in significantly smaller and faster applications.
react
An npm package to get you immediate access to React,
without also requiring the JSX transformer. This is especially useful for cases where you
want to browserify
your module using
React
.
Note: by default, React will be in development mode. The development version includes extra warnings about common mistakes, whereas the production version includes extra performance optimizations and strips all error messages.
To use React in production mode, set the environment variable NODE_ENV
to production
. A minifier that performs dead-code elimination such as UglifyJS is recommended to completely remove the extra code present in development mode.
Example Usage
var React = require('react');
var createFragment = require('react-addons-create-fragment');
var immutabilityHelpers = require('react-addons-update');
var CSSTransitionGroup = require('react-addons-css-transition-group');
For a complete list of addons visit the addons documentation page.
15.0.0 (April 7, 2016)
Major changes
- Initial render now uses
document.createElement
instead of generating HTML. Previously we would generate a large string of HTML and then set node.innerHTML
. At the time, this was decided to be faster than using document.createElement
for the majority of cases and browsers that we supported. Browsers have continued to improve and so overwhelmingly this is no longer true. By using createElement
we can make other parts of React faster. (@sophiebits in #5205) data-reactid
is no longer on every node. As a result of using document.createElement
, we can prime the node cache as we create DOM nodes, allowing us to skip a potential lookup (which used the data-reactid
attribute). Root nodes will have a data-reactroot
attribute and server generated markup will still contain data-reactid
. (@sophiebits in #5205)- No more extra
<span>
s. ReactDOM will now render plain text nodes interspersed with comment nodes that are used for demarcation. This gives us the same ability to update individual pieces of text, without creating extra nested nodes. If you were targeting these <span>
s in your CSS, you will need to adjust accordingly. You can always render them explicitly in your components. (@mwiencek in #5753) - Rendering
null
now uses comment nodes. Previously null
would render to <noscript>
elements. We now use comment nodes. This may cause issues if making use of :nth-child
CSS selectors. While we consider this rendering behavior an implementation detail of React, it's worth noting the potential problem. (@sophiebits in #5451) - Functional components can now return
null
. We added support for defining stateless components as functions in React 0.14. However, React 0.14 still allowed you to define a class component without extending React.Component
or using React.createClass()
, so we couldn’t reliably tell if your component is a function or a class, and did not allow returning null
from it. This issue is solved in React 15, and you can now return null
from any component, whether it is a class or a function. (@jimfb in #5884) - Improved SVG support. All SVG tags are now fully supported. (Uncommon SVG tags are not present on the
React.DOM
element helper, but JSX and React.createElement
work on all tag names.) All SVG attributes that are implemented by the browsers should be supported too. If you find any attributes that we have missed, please let us know in this issue. (@zpao in #6243)
Breaking changes
- No more extra
<span>
s. React.cloneElement()
now resolves defaultProps
. We fixed a bug in React.cloneElement()
that some components may rely on. If some of the props
received by cloneElement()
are undefined
, it used to return an element with undefined
values for those props. We’re changing it to be consistent with createElement()
. Now any undefined
props passed to cloneElement()
are resolved to the corresponding component’s defaultProps
. (@truongduy134 in #5997)ReactPerf.getLastMeasurements()
is opaque. This change won’t affect applications but may break some third-party tools. We are revamping ReactPerf
implementation and plan to release it during the 15.x cycle. The internal performance measurement format is subject to change so, for the time being, we consider the return value of ReactPerf.getLastMeasurements()
an opaque data structure that should not be relied upon. (@gaearon in #6286)
Removed deprecations
These deprecations were introduced nine months ago in v0.14 with a warning and are removed:
- Deprecated APIs are removed from the
React
top-level export: findDOMNode
, render
, renderToString
, renderToStaticMarkup
, and unmountComponentAtNode
. As a reminder, they are now available on ReactDOM
and ReactDOMServer
. (@jimfb in #5832) - Deprecated addons are removed:
batchedUpdates
and cloneWithProps
. (@jimfb in #5859, @zpao in #6016) - Deprecated component instance methods are removed:
setProps
, replaceProps
, and getDOMNode
. (@jimfb in #5570) - Deprecated CommonJS
react/addons
entry point is removed. As a reminder, you should use separate react-addons-*
packages instead. This only applies if you use the CommonJS builds. (@gaearon in #6285) - Passing
children
to void elements like <input>
was deprecated, and now throws an error. (@jonhester in #3372) - React-specific properties on DOM
refs
(e.g. this.refs.div.props
) were deprecated, and are removed now. (@jimfb in #5495)
New deprecations, introduced with a warning
Each of these changes will continue to work as before with a new warning until the release of React 16 so you can upgrade your code gradually.
LinkedStateMixin
and valueLink
are now deprecated due to very low popularity. If you need this, you can use a wrapper component that implements the same behavior: react-linked-input. (@jimfb in #6127)- Future versions of React will treat
<input value={null}>
as a request to clear the input. However, React 0.14 has been ignoring value={null}
. React 15 warns you on a null
input value and offers you to clarify your intention. To fix the warning, you may explicitly pass an empty string to clear a controlled input, or pass undefined
to make the input uncontrolled. (@antoaravinth in #5048) ReactPerf.printDOM()
was renamed to ReactPerf.printOperations()
, and ReactPerf.getMeasurementsSummaryMap()
was renamed to ReactPerf.getWasted()
. (@gaearon in #6287)
New helpful warnings
- If you use a minified copy of the development build, React DOM kindly encourages you to use the faster production build instead. (@sophiebits in #5083)
- React DOM: When specifying a unit-less CSS value as a string, a future version will not add
px
automatically. This version now warns in this case (ex: writing style={{width: '300'}}
. Unitless number values like width: 300
are unchanged. (@pluma in #5140) - Synthetic Events will now warn when setting and accessing properties (which will not get cleared appropriately), as well as warn on access after an event has been returned to the pool. (@kentcdodds in #5940 and @koba04 in #5947)
- Elements will now warn when attempting to read
ref
and key
from the props. (@prometheansacrifice in #5744) - React will now warn if you pass a different
props
object to super()
in the constructor. (@prometheansacrifice in #5346) - React will now warn if you call
setState()
inside getChildContext()
. (@raineroviir in #6121) - React DOM now attempts to warn for mistyped event handlers on DOM elements, such as
onclick
which should be onClick
. (@ali in #5361) - React DOM now warns about
NaN
values in style
. (@jontewks in #5811) - React DOM now warns if you specify both
value
and defaultValue
for an input. (@mgmcdermott in #5823) - React DOM now warns if an input switches between being controlled and uncontrolled. (@TheBlasfem in #5864)
- React DOM now warns if you specify
onFocusIn
or onFocusOut
handlers as they are unnecessary in React. (@jontewks in #6296) - React now prints a descriptive error message when you pass an invalid callback as the last argument to
ReactDOM.render()
, this.setState()
, or this.forceUpdate()
. (@conorhastings in #5193 and @gaearon in #6310) - Add-Ons:
TestUtils.Simulate()
now prints a helpful message if you attempt to use it with shallow rendering. (@conorhastings in #5358) - PropTypes:
arrayOf()
and objectOf()
provide better error messages for invalid arguments. (@chicoxyzzy in #5390)
Notable bug fixes
- Fixed multiple small memory leaks. (@sophiebits in #4983 and @victor-homyakov in #6309)
- Input events are handled more reliably in IE 10 and IE 11; spurious events no longer fire when using a placeholder. (@jquense in #4051)
- The
componentWillReceiveProps()
lifecycle method is now consistently called when context
changes. (@milesj in #5787) React.cloneElement()
doesn’t append slash to an existing key
when used inside React.Children.map()
. (@ianobermiller in #5892)- React DOM now supports the
cite
and profile
HTML attributes. (@AprilArcus in #6094 and @saiichihashimoto in #6032) - React DOM now supports
cssFloat
, gridRow
and gridColumn
CSS properties. (@stevenvachon in #6133 and @mnordick in #4779) - React DOM now correctly handles
borderImageOutset
, borderImageWidth
, borderImageSlice
, floodOpacity
, strokeDasharray
, and strokeMiterlimit
as unitless CSS properties. (@rofrischmann in #6210 and #6270) - React DOM now supports the
onAnimationStart
, onAnimationEnd
, onAnimationIteration
, onTransitionEnd
, and onInvalid
events. Support for onLoad
has been added to object
elements. (@tomduncalf in #5187, @milesj in #6005, and @ara4n in #5781) - React DOM now defaults to using DOM attributes instead of properties, which fixes a few edge case bugs. Additionally the nullification of values (ex:
href={null}
) now results in the forceful removal, no longer trying to set to the default value used by browsers in the absence of a value. (@syranide in #1510) - React DOM does not mistakenly coerce
children
to strings for Web Components. (@jimfb in #5093) - React DOM now correctly normalizes SVG
<use>
events. (@edmellum in #5720) - React DOM does not throw if a
<select>
is unmounted while its onChange
handler is executing. (@sambev in #6028) - React DOM does not throw in Windows 8 apps. (@Andrew8xx8 in #6063)
- React DOM does not throw when asynchronously unmounting a child with a
ref
. (@yiminghe in #6095) - React DOM no longer forces synchronous layout because of scroll position tracking. (@syranide in #2271)
Object.is
is used in a number of places to compare values, which leads to fewer false positives, especially involving NaN
. In particular, this affects the shallowCompare
add-on. (@chicoxyzzy in #6132)- Add-Ons: ReactPerf no longer instruments adding or removing an event listener because they don’t really touch the DOM due to event delegation. (@antoaravinth in #5209)
Other improvements
- React now uses
loose-envify
instead of envify
so it installs fewer transitive dependencies. (@qerub in #6303) - Shallow renderer now exposes
getMountedInstance()
. (@glenjamin in #4918) - Shallow renderer now returns the rendered output from
render()
. (@simonewebdesign in #5411) - React no longer depends on ES5 shams for
Object.create
and Object.freeze
in older environments. It still, however, requires ES5 shims in those environments. (@dgreensp in #4959) - React DOM now allows
data-
attributes with names that start with numbers. (@nLight in #5216) - React DOM adds a new
suppressContentEditableWarning
prop for components like Draft.js that intentionally manage contentEditable
children with React. (@mxstbr in #6112) - React improves the performance for
createClass()
on complex specs. (@sophiebits in #5550)