问题9 slate 添加图片使用了emotion

emotion是什么？
在4.2K星级，Emotion是一个高性能且灵活的CSS-in-JS库，允许您使用字符串或对象样式设置应用程序样式。它具有可预测的组合，以避免CSS的特殊性问题。基于glam 库及其理念，我们的想法是通过使用babel和PostCSS解析样式来编写CSS时保持运行时性能。核心运行时为2.3kb，React支持为4kb。

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slate文档源码

import { Editor, getEventTransfer } from 'slate-react'
import { Block, Value } from 'slate'

import React from 'react'
import initialValueAsJson from './value.json'
import imageExtensions from 'image-extensions'
import isUrl from 'is-url'
import { css } from 'emotion'
import { Button, Icon, Toolbar } from '../components'

/**
 * Deserialize the initial editor value.
 *
 * @type {Object}
 */

const initialValue = Value.fromJSON(initialValueAsJson)

/**
 * A function to determine whether a URL has an image extension.
 *
 * @param {String} url
 * @return {Boolean}
 */

function isImage(url) {
  return imageExtensions.includes(getExtension(url))
}

/**
 * Get the extension of the URL, using the URL API.
 *
 * @param {String} url
 * @return {String}
 */

function getExtension(url) {
  return new URL(url).pathname.split('.').pop()
}

/**
 * A change function to standardize inserting images.
 *
 * @param {Editor} editor
 * @param {String} src
 * @param {Range} target
 */

function insertImage(editor, src, target) {
  if (target) {
    editor.select(target)
  }

  editor.insertBlock({
    type: 'image',
    data: { src },
  })
}

/**
 * The editor's schema.
 *
 * @type {Object}
 */

const schema = {
  document: {
    last: { type: 'paragraph' },
    normalize: (editor, { code, node, child }) => {
      switch (code) {
        case 'last_child_type_invalid': {
          const paragraph = Block.create('paragraph')
          return editor.insertNodeByKey(node.key, node.nodes.size, paragraph)
        }
      }
    },
  },
  blocks: {
    image: {
      isVoid: true,
    },
  },
}

/**
 * The images example.
 *
 * @type {Component}
 */

class Images extends React.Component {
  /**
   * Store a reference to the `editor`.
   *
   * @param {Editor} editor
   */

  ref = editor => {
    this.editor = editor
  }

  /**
   * Render the app.
   *
   * @return {Element} element
   */

  render() {
    return (
      <div>
        <Toolbar>
          <Button onMouseDown={this.onClickImage}>
            <Icon>image</Icon>
          </Button>
        </Toolbar>
        <Editor
          placeholder="Enter some text..."
          ref={this.ref}
          defaultValue={initialValue}
          schema={schema}
          onDrop={this.onDropOrPaste}
          onPaste={this.onDropOrPaste}
          renderBlock={this.renderBlock}
        />
      </div>
    )
  }

  /**
   * Render a Slate block.
   *
   * @param {Object} props
   * @return {Element}
   */

  renderBlock = (props, editor, next) => {
    const { attributes, node, isFocused } = props

    switch (node.type) {
      case 'image': {
        const src = node.data.get('src')
        return (
          <img
            {...attributes}
            src={src}
            className={css`
              display: block;
              max-width: 100%;
              max-height: 20em;
              box-shadow: ${isFocused ? '0 0 0 2px blue;' : 'none'};
            `}
          />
        )
      }

      default: {
        return next()
      }
    }
  }

  /**
   * On clicking the image button, prompt for an image and insert it.
   *
   * @param {Event} event
   */

  onClickImage = event => {
    event.preventDefault()
    const src = window.prompt('Enter the URL of the image:')
    if (!src) return
    this.editor.command(insertImage, src)
  }

  /**
   * On drop, insert the image wherever it is dropped.
   *
   * @param {Event} event
   * @param {Editor} editor
   * @param {Function} next
   */

  onDropOrPaste = (event, editor, next) => {
    const target = editor.findEventRange(event)
    if (!target && event.type === 'drop') return next()

    const transfer = getEventTransfer(event)
    const { type, text, files } = transfer

    if (type === 'files') {
      for (const file of files) {
        const reader = new FileReader()
        const [mime] = file.type.split('/')
        if (mime !== 'image') continue

        reader.addEventListener('load', () => {
          editor.command(insertImage, reader.result, target)
        })

        reader.readAsDataURL(file)
      }
      return
    }

    if (type === 'text') {
      if (!isUrl(text)) return next()
      if (!isImage(text)) return next()
      editor.command(insertImage, text, target)
      return
    }

    next()
  }
}

/**
 * Export.
 */

export default Images