组件
组件
import React from 'react'
import ReactDOM from 'react-dom'
class Hello extends React.Component {
render () {
return <div className='message-box'>
Hello {this.props.name}
</div>
}
}
const el = document.body
ReactDOM.render(<Hello name='John' />, el)
Use the React.js jsfiddle to start hacking. (or the unofficial jsbin)
属性
<Video fullscreen={true} />
render () {
this.props.fullscreen
···
}
使用 this.props
访问从组件传入的属性。
参考: Properties
状态
this.setState({ username: 'rstacruz' })
render () {
this.state.username
···
}
使用状态 (this.state
) 管理动态数据。
参考: States
Nesting
class Info extends React.Component {
render () {
const { avatar, username } = this.props
return <div>
<UserAvatar src={avatar} />
<UserProfile username={username} />
</div>
}
}
Nest components to separate concerns.
Children
<AlertBox>
<h1>You have pending notifications</h1>
</AlertBox>
class AlertBox extends React.Component {
render () {
return <div className='alert-box'>
{this.props.children}
</div>
}
}
Children are passed as the children
property.
Defaults
Setting default props
Hello.defaultProps = {
color: 'blue'
}
See: defaultProps
Setting default state
class Hello extends React.Component {
constructor (props) {
super(props)
this.state = { visible: true }
}
}
Set the default state in the constructor()
.
See: Setting the default state
Other components
Function components
function MyComponent ({ name }) {
return <div className='message-box'>
Hello {name}
</div>
}
Functional components have no state. Also, their props
are passed as the first parameter to a function.
See: Function and Class Components
Pure components
class MessageBox extends React.PureComponent {
···
}
Performance-optimized version of React.Component
. Doesn’t rerender if props/state hasn’t changed.
See: Pure components
Component API
this.forceUpdate()
this.setState({ ... })
this.state
this.props
These methods and properies are available for Component
instances.
See: Component API
Lifecycle
Mounting
Method | Description |
---|---|
constructor (props) |
Before rendering # |
componentWillMount() |
Don’t use this # |
render() |
Render # |
componentDidMount() |
After rendering (DOM available) # |
componentWillUnmount() |
Before DOM removal # |
componentDidCatch() |
Catch errors (16+) # |
Set initial the state on constructor()
.
Add DOM event handlers, timers (etc) on componentDidMount()
, then remove them on componentWillUnmount()
.
Updating
Method | Description |
---|---|
componentWillReceiveProps (newProps) |
Use setState() here |
shouldComponentUpdate (newProps, newState) |
Skips render() if returns false |
componentWillUpdate (newProps, newState) |
Can’t use setState() here |
render() |
Render |
componentDidUpdate (prevProps, prevState) |
Operate on the DOM here |
Called when parents change properties and .setState()
. These are not called for initial renders.
See: Component specs
DOM nodes
References
class MyComponent extends React.Component {
render () {
return <div>
<input ref={el => this.input = el} />
</div>
}
componentDidMount () {
this.input.focus()
}
}
Allows access to DOM nodes.
See: Refs and the DOM
DOM Events
class MyComponent extends React.Component {
render () {
<input type="text"
value={this.state.value}
onChange={event => this.onChange(event)} />
}
onChange (event) {
this.setState({ value: event.target.vlaue })
}
}
Pass functions to attributes like onChange
.
See: Events
Other features
Transfering props
<VideoPlayer src="video.mp4" />
class VideoPlayer extends React.Component {
render () {
return <VideoEmbed {...this.props} />
}
}
Propagates src="..."
down to the sub-component.
Top-level API
React.createClass({ ... })
React.isValidElement(c)
ReactDOM.render(<Component />, domnode, [callback])
ReactDOM.unmountComponentAtNode(domnode)
ReactDOMServer.renderToString(<Component />)
ReactDOMServer.renderToStaticMarkup(<Component />)
There are more, but these are most common.
See: React top-level API
JSX patterns
Style shorthand
var style = { height: 10 }
return <div style={style}></div>
return <div style={{ margin: 0, padding: 0 }}></div>
See: Inline styles
Inner HTML
function markdownify() { return "<p>...</p>"; }
<div dangerouslySetInnerHTML={{__html: markdownify()}} />
See: Dangerously set innerHTML
Lists
class TodoList extends React.Component {
render () {
const { items } = this.props
return <ul>
{items.map(item =>
<TodoItem item={item} key={item.key} />)}
</ul>
}
}
Always supply a key
property.
Conditionals
<div>
{showPopup
? <Popup />
: null}
</div>
New features
Returning fragments
render () {
// Don't forget the keys!
return [
<li key="A">First item</li>,
<li key="B">Second item</li>
]
}
You can return multiple nodes as arrays.
Errors
class MyComponent extends React.Component {
···
componentDidCatch (error, info) {
this.setState({ error })
}
}
Catch errors via componentDidCatch
. (React 16+)
See: Error handling in React 16
Portals
render () {
return React.createPortal(
this.props.children,
document.getElementById('menu')
)
}
This renders this.props.children
into any location in the DOM.
See: Portals
Hydration
const el = document.getElementById('app')
ReactDOM.hydrate(<App />, el)
Use ReactDOM.hydrate
instead of using ReactDOM.render
if you’re rendering over the output of ReactDOMServer.
See: Hydrate
Property validation
PropTypes
import PropTypes from 'prop-types'
See: Typechecking with PropTypes
any |
Anything |
Basic
string |
|
number |
|
func |
Function |
bool |
True or false |
Enum
oneOf (any) |
Enum types |
oneOfType (type array) |
Union |
Array
array |
|
arrayOf (…) |
Object
object |
|
objectOf (…) |
Object with values of a certain type |
instanceOf (…) |
Instance of a class |
shape (…) |
Elements
element |
React element |
node |
DOM node |
Required
(···).isRequired |
Required |
Basic types
MyComponent.propTypes = {
email: PropTypes.string,
seats: PropTypes.number,
callback: PropTypes.func,
isClosed: PropTypes.bool,
any: PropTypes.any
}
Required types
MyCo.propTypes = {
name: PropTypes.string.isRequired
}
Elements
MyCo.propTypes = {
// React element
element: PropTypes.element,
// num, string, element, or an array of those
node: PropTypes.node
}
Enumerables (oneOf)
MyCo.propTypes = {
direction: PropTypes.oneOf([
'left', 'right'
])
}
Arrays and objects
MyCo.propTypes = {
list: PropTypes.array,
ages: PropTypes.arrayOf(PropTypes.number),
user: PropTypes.object,
user: PropTypes.objectOf(PropTypes.number),
message: PropTypes.instanceOf(Message)
}
MyCo.propTypes = {
user: PropTypes.shape({
name: PropTypes.string,
age: PropTypes.number
})
}
Use .array[Of]
, .object[Of]
, .instanceOf
, .shape
.
Custom validation
MyCo.propTypes = {
customProp: (props, key, componentName) => {
if (!/matchme/.test(props[key])) {
return new Error('Validation failed!')
}
}
}
Also see
- React website (reactjs.org)
- React cheatsheet (reactcheatsheet.com)
- Awesome React (github.com)
- React v0.14 cheatsheet Legacy version