原文：Our Best Practices for Writing React Components .
这里意译。有些点在之前的文章里提到过： #2

如果组件带有state或者方法，就使用Class写法。

Class写法

如果组件带有state或者方法，就使用Class写法。

1. 引入CSS

import React, { Component } from 'react'
import { observer } from 'mobx-react'
import ExpandableForm from './ExpandableForm'
import './styles/ProfileContainer.css'

2. 初始化State

使用ES7句法定义state

import React, { Component } from 'react'
import { observer } from 'mobx-react'
import ExpandableForm from './ExpandableForm'
import './styles/ProfileContainer.css'
export default class ProfileContainer extends Component {
  state = { expanded: false }

3. 初始化`propTypes`和`defaultProps`

import React, { Component } from 'react'
import { observer } from 'mobx-react'
import { string, object } from 'prop-types'
import ExpandableForm from './ExpandableForm'
import './styles/ProfileContainer.css'
export default class ProfileContainer extends Component {
  state = { expanded: false }
 
  static propTypes = {
    model: object.isRequired,
    title: string
  }
 
  static defaultProps = {
    model: {
      id: 0
    },
    title: 'Your Name'
  }

propTypes和defaultProps的声明应该置顶便于其他开发者阅读。在React v15.3.0版本，推荐使用prop-types这个包替代React.PropTypes。
重要的一点：所有的组件都应当有propTypes验证。

4. 组件内的方法

import React, { Component } from 'react'
import { observer } from 'mobx-react'
import { string, object } from 'prop-types'
import ExpandableForm from './ExpandableForm'
import './styles/ProfileContainer.css'
export default class ProfileContainer extends Component {
  state = { expanded: false }
 
  static propTypes = {
    model: object.isRequired,
    title: string
  }
 
  static defaultProps = {
    model: {
      id: 0
    },
    title: 'Your Name'
  }
  handleSubmit = (e) => {
    e.preventDefault()
    this.props.model.save()
  }
  
  handleNameChange = (e) => {
    this.props.model.changeName(e.target.value)
  }
  
  handleExpand = (e) => {
    e.preventDefault()
    this.setState({ expanded: !this.state.expanded })
  }

使用在方法中箭头函数来替代this.handleExpand.bind(this)

5. `this.setState()`是异步的。应该使用函数入参

this.setState(prevState => ({ expanded: !prevState.expanded }))

6. 一个组件或者元素含有多个`props`应当分行写

render() {
    const {
      model,
      title
    } = this.props
    return ( 
      <ExpandableForm 
        onSubmit={this.handleSubmit} 
        expanded={this.state.expanded} 
        onExpand={this.handleExpand}>
        <div>
          <h1>{title}</h1>
          <input
            type="text"
            value={model.name}
            onChange={this.handleNameChange}
            placeholder="Your Name"/>
        </div>
      </ExpandableForm>
    )
  }

7. 避免在子组件中使用闭包

 <input
           type="text"
            value={model.name}
            // onChange={(e) => { model.name = e.target.value }}
            // ^ Not this. Use the below:
            onChange={this.handleChange}
            placeholder="Your Name"/>

8.完整的`class`组件写法

import React, { Component } from 'react'
import { observer } from 'mobx-react'
import { string, object } from 'prop-types'
// 分开本地导入和依赖导入
import ExpandableForm from './ExpandableForm'
import './styles/ProfileContainer.css'

// 使用修饰器（如果有的话）
@observer
export default class ProfileContainer extends Component {
  state = { expanded: false }
  // 初始化state (ES7) 或者在构造函数(constructor)中初始化state (ES6)
 
  //使用静态属性(ES7)声明propTypes越早越好
  static propTypes = {
    model: object.isRequired,
    title: string
  }

  // 在propTypes后声明defaultProps
  static defaultProps = {
    model: {
      id: 0
    },
    title: 'Your Name'
  }

  // 使用箭头函数绑定指向定义的上下文的this
  handleSubmit = (e) => {
    e.preventDefault()
    this.props.model.save()
  }
  
  handleNameChange = (e) => {
    this.props.model.name = e.target.value
  }
  
  handleExpand = (e) => {
    e.preventDefault()
    this.setState(prevState => ({ expanded: !prevState.expanded }))
  }
  
  render() {
    // 解构props成可读的
    const {
      model,
      title
    } = this.props
    return ( 
      <ExpandableForm 
        onSubmit={this.handleSubmit} 
        expanded={this.state.expanded} 
        onExpand={this.handleExpand}>
        // 如果有2个以上props,分行写
        <div>
          <h1>{title}</h1>
          <input
            type="text"
            value={model.name}
            // onChange={(e) => { model.name = e.target.value }}
            // 避免创造新的闭包，应该使用下面的方法。
            onChange={this.handleNameChange}
            placeholder="Your Name"/>
        </div>
      </ExpandableForm>
    )
  }
}

函数式组件写法

1. propTypes

import React from 'react'
import { observer } from 'mobx-react'
import { func, bool } from 'prop-types'
import './styles/Form.css'
ExpandableForm.propTypes = {
  onSubmit: func.isRequired,
  expanded: bool
}
// Component declaration

2. Destructuring Props and defaultProps

import React from 'react'
import { observer } from 'mobx-react'
import { func, bool } from 'prop-types'
import './styles/Form.css'
ExpandableForm.propTypes = {
  onSubmit: func.isRequired,
  expanded: bool,
  onExpand: func.isRequired
}
function ExpandableForm(props) {
  const formStyle = props.expanded ? {height: 'auto'} : {height: 0}
  return (
    <form style={formStyle} onSubmit={props.onSubmit}>
      {props.children}
      <button onClick={props.onExpand}>Expand</button>
    </form>
  )
}

结合ES6的函数入参解构，可以如下书写

import React from 'react'
import { observer } from 'mobx-react'
import { func, bool } from 'prop-types'
import './styles/Form.css'
ExpandableForm.propTypes = {
  onSubmit: func.isRequired,
  expanded: bool,
  onExpand: func.isRequired
}
function ExpandableForm({ onExpand, expanded = false, children, onSubmit }) {
  const formStyle = expanded ? {height: 'auto'} : {height: 0}
  return (
    <form style={formStyle} onSubmit={onSubmit}>
      {children}
      <button onClick={onExpand}>Expand</button>
    </form>
  )
}

3. 避免箭头函数写法

const ExpandableForm = ({ onExpand, expanded, children }) => {

虽然语法没问题，但是这里函数是匿名函数。

4. 高阶组件

import React from 'react'
import { observer } from 'mobx-react'
import { func, bool } from 'prop-types'
import './styles/Form.css'
ExpandableForm.propTypes = {
  onSubmit: func.isRequired,
  expanded: bool,
  onExpand: func.isRequired
}
function ExpandableForm({ onExpand, expanded = false, children, onSubmit }) {
  const formStyle = expanded ? {height: 'auto'} : {height: 0}
  return (
    <form style={formStyle} onSubmit={onSubmit}>
      {children}
      <button onClick={onExpand}>Expand</button>
    </form>
  )
}
export default observer(ExpandableForm)

5. 完整代码

import React from 'react'
import { observer } from 'mobx-react'
import { func, bool } from 'prop-types'
// Separate local imports from dependencies
import './styles/Form.css'

// 在组件前声明propTypes
ExpandableForm.propTypes = {
  onSubmit: func.isRequired,
  expanded: bool,
  onExpand: func.isRequired
}

// 解构props,通过函数入参默认值的方式设定defaultProps
function ExpandableForm({ onExpand, expanded = false, children, onSubmit }) {
  const formStyle = expanded ? { height: 'auto' } : { height: 0 }
  return (
    <form style={formStyle} onSubmit={onSubmit}>
      {children}
      <button onClick={onExpand}>Expand</button>
    </form>
  )
}

// Wrap the component instead of decorating it
export default observer(ExpandableForm)