Code

editor-component.tsx

import 'prosekit/basic/style.css'

import type { Editor } from 'prosekit/core'
import { ProseKit, useDocChange } from 'prosekit/react'

export default function EditorComponent({
  editor,
  onDocChange,
}: {
  editor: Editor
  onDocChange: () => void
}) {
  useDocChange(onDocChange, { editor })

  return (
    <ProseKit editor={editor}>
      <div className='relative w-full flex-1 box-border overflow-y-scroll'>
        <div ref={editor.mount} className='ProseMirror box-border min-h-full px-[max(4rem,_calc(50%-20rem))] py-8 outline-none outline-0 [&_span[data-mention="user"]]:text-blue-500 [&_span[data-mention="tag"]]:text-violet-500 [&_pre]:text-white [&_pre]:bg-zinc-800'></div>
      </div>
    </ProseKit>
  )
}

editor.tsx

import 'prosekit/basic/style.css'

import { defineBasicExtension } from 'prosekit/basic'
import {
  createEditor,
  htmlFromNode,
  jsonFromHTML,
  type NodeJSON,
} from 'prosekit/core'
import { ListDOMSerializer } from 'prosekit/extensions/list'
import { useCallback, useMemo, useState } from 'react'

import EditorComponent from './editor-component'
import { htmlFromMarkdown, markdownFromHTML } from './markdown'

export default function Editor() {
  const [defaultContent, setDefaultContent] = useState<NodeJSON | undefined>()
  const [records, setRecords] = useState<string[]>([])
  const [hasUnsavedChange, setHasUnsavedChange] = useState(false)
  const [key, setKey] = useState(1)

  // Create a new editor instance whenever `defaultContent` changes
  const editor = useMemo(() => {
    const extension = defineBasicExtension()
    return createEditor({ extension, defaultContent })
  }, [defaultContent])

  // Enable the save button
  const handleDocChange = useCallback(() => setHasUnsavedChange(true), [])

  // Save the current document as a Markdown string
  const handleSave = useCallback(() => {
    const html = htmlFromNode(editor.view.state.doc, {
      DOMSerializer: ListDOMSerializer,
    })
    const record = markdownFromHTML(html)
    setRecords((records) => [...records, record])
    setHasUnsavedChange(false)
  }, [editor])

  // Load a document from a Markdown string
  const handleLoad = useCallback(
    (record: string) => {
      const html = htmlFromMarkdown(record)
      setDefaultContent(jsonFromHTML(html, { schema: editor.schema }))
      setHasUnsavedChange(false)
      setKey((key) => key + 1)
    },
    [editor.schema],
  )

  return (
    <div className='box-border h-full w-full min-h-36 overflow-y-hidden overflow-x-hidden rounded-md border border-solid border-gray-200 shadow dark:border-zinc-700 flex flex-col bg-white dark:bg-neutral-900'>
      <button
        onClick={handleSave}
        disabled={!hasUnsavedChange}
        className="m-1 border border-solid bg-white px-2 py-1 text-sm text-black disabled:cursor-not-allowed disabled:text-gray-500"
      >
        {hasUnsavedChange ? 'Save' : 'No changes to save'}
      </button>
      <ul className="border-b border-t border-solid text-sm">
        {records.map((record, index) => (
          <li key={index} className="m-1 flex gap-2">
            <button
              className="border border-solid bg-white px-2 py-1 text-black"
              onClick={() => handleLoad(record)}
            >
              Load
            </button>
            <span className="flex-1 overflow-x-scroll p-2">
              <pre>{record}</pre>
            </span>
          </li>
        ))}
      </ul>
      <EditorComponent
        key={key}
        editor={editor}
        onDocChange={handleDocChange}
      />
    </div>
  )
}

markdown.ts

import rehypeParse from 'rehype-parse'
import rehypeRemark from 'rehype-remark'
import remarkHtml from 'remark-html'
import remarkParse from 'remark-parse'
import remarkStringify from 'remark-stringify'
import { unified } from 'unified'

export function markdownFromHTML(html: string): string {
  return unified()
    .use(rehypeParse)
    .use(rehypeRemark)
    .use(remarkStringify)
    .processSync(html)
    .toString()
}

export function htmlFromMarkdown(markdown: string): string {
  return unified()
    .use(remarkParse)
    .use(remarkHtml)
    .processSync(markdown)
    .toString()
}