首先来看下 vue 的 slot 的实现

<base-layout> 组件，具名插槽 name 定义以及默认插槽

<div class="container">
  <header>
    <slot name="header"></slot>
  </header>
  <main>
    <slot></slot>
  </main>
  <footer>
    <slot name="footer"></slot>
  </footer>
</div>

<template> 提供内容渲染的组件

<base-layout>
  <template v-slot:header>
    <h1>Here might be a page title</h1>
  </template>

  <p>A paragraph for the main content.</p>
  <p>And another one.</p>

  <template v-slot:footer>
    <p>Here's some contact info</p>
  </template>
</base-layout>

最终会渲染出已下架结构

<div class="container">
  <header>
    <h1>Here might be a page title</h1>
  </header>
  <main>
    <p>A paragraph for the main content.</p>
    <p>And another one.</p>
  </main>
  <footer>
    <p>Here's some contact info</p>
  </footer>
</div>

言归正传，怎样使用 react 的 context 实现 vue 的这一功能呢

1 首先确认下 layout 组件的结构

import React, {Component} from 'react';
import SlotProvider from './SlotProvider'
import Slot from './Slot'

class AppLayout extends Component {
  static displayName = 'AppLayout'
  
  render () {
    return (
      <div className="container">
        <header>
          <Slot name="header"></Slot>
        </header>
        <main>
          <Slot></Slot>
        </main>
        <footer>
          <Slot name="footer"></Slot>
        </footer>
      </div>
    )
  }
}

export default SlotProvider(AppLayout)

2 对此结构输出具体内容的组件

import React, {Component} from 'react';
import AppLayout from './AppLayout'
import AddOn from './AddOn'
export default class App extends Component {render() {
        return (
            <AppLayout>
                <AddOn slot="header">
                    <h1> 这里可能是一个页面标题 </h1>
                </AddOn>
                <AddOn>
                    <p> 主要内容的一个段落。</p>
                    <p> 另一个段落。</p>
                </AddOn>
                <AddOn slot="footer">
                    <p> 这里有一些联系信息 </p>
                </AddOn>
            </AppLayout>
        )
    }
}

3 其中 AddOn 类似于上面 vue 的 template，所以下面来实现这个简单的只是用来提供 slot 标识和 children 内容的组件 AddOn 的实现

import React from 'react';
import PropTypes from 'prop-types'
const AddOn = () => null

AddOn.propTypes = {slot: PropTypes.string}
AddOn.defaultTypes = {slot: '$$default'}
AddOn.displayName = 'AddOn'
export default AddOn

4 Slot 组件

import React from 'react';
import {SlotContext} from './SlotProvider'
import PropTypes from 'prop-types'

const Slot = ({name, children}) => {
  return (
    <SlotContext.Consumer>
      {(value) => {const addOnRenderer = value.requestAddOnRenderer(name)
          return (addOnRenderer && addOnRenderer()) || children || null
      }}
    </SlotContext.Consumer>
  )
}

Slot.displayName = 'Slot'
Slot.propTypes = {name: PropTypes.string}
Slot.defaultProps = {name: '$$default'}
export default Slot

5 接下来就是对 Slot 进行解析的 HOC SlotProvider 组件了

import React, {Component} from 'react';


function getDisplayName(component) {return component.displayName || component.name || 'component'}

export const SlotContext = React.createContext({requestAddOnRenderer: () => {}})

const SlotProviderHoC = (WrappedComponent) => {
    return class extends Component {static displayName = `SlotProvider(${getDisplayName(WrappedComponent)})`

        // 用于缓存每个 <AddOn /> 的内容
        addOnRenderers = {}

        requestAddOnRenderer = (name) => {if (!this.addOnRenderers[name]) {return undefined}
            return () => (this.addOnRenderers[name]
            )
        }

        render() {
            const {
                children,
                ...restProps
            } = this.props

            if (children) {
                // 以 k - v 的方式缓存 <AddOn /> 的内容
                const arr = React.Children.toArray(children)
                const nameChecked = []
                this.addOnRenderers = {}
                arr.forEach(item => {
                    const itemType = item.type
                    console.log('itemType',itemType)
                    if (item.type.displayName === 'AddOn') {
                        const slotName = item.props.slot || '$$default'
                        // 确保内容唯一性
                        if (nameChecked.findIndex(item => item === slotName) !== -1) {throw new Error(`Slot(${slotName}) has been occupied`)
                        }
                        this.addOnRenderers[slotName] = item.props.children
                        nameChecked.push(slotName)
                    }
                })
            }

            return (<SlotContext.Provider value={{ requestAddOnRenderer: this.requestAddOnRenderer}}>
                    <WrappedComponent {...restProps} />
                </SlotContext.Provider >
            )
        }
    }
  }

  export default SlotProviderHoC

6 最终渲染结果

摘抄：张国钰