Code

editor-component.tsx

import 'prosekit/basic/style.css'

import { defineBasicExtension } from 'prosekit/basic'
import { createEditor } from 'prosekit/core'
import { ProseKit } from 'prosekit/react'
import { useMemo } from 'react'

import ExtensionComponent from './extension-component'

export default function EditorComponent({
  placeholder,
}: {
  placeholder: string
}) {
  const editor = useMemo(() => {
    return createEditor({ extension: defineBasicExtension() })
  }, [])

  return (
    <ProseKit editor={editor}>
      <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'>
        <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>
      </div>
      <ExtensionComponent placeholder={placeholder} />
    </ProseKit>
  )
}

editor.tsx

import { useCallback, useEffect, useRef, useState } from 'react'

import EditorComponent from './editor-component'

function EditorGroup() {
  const nextKeyRef = useRef(1)
  const [editorKeys, setEditorKeys] = useState<number[]>([])

  const addEditor = useCallback(() => {
    const key = nextKeyRef.current
    nextKeyRef.current += 1
    setEditorKeys((keys) => [...keys, key])
  }, [])

  const removeEditor = useCallback((key: number) => {
    setEditorKeys((keys) => keys.filter((k) => k !== key))
  }, [])

  useEffect(() => {
    if (nextKeyRef.current === 1) {
      addEditor()
    }
  }, [addEditor])

  return (
    <div className="flex flex-col gap-2">
      <div className="flex gap-2">
        <button onClick={addEditor} className="border p-2">
          Add editor
        </button>
        {editorKeys.map((key) => (
          <button
            key={key}
            onClick={() => removeEditor(key)}
            className="border p-2"
          >
            Unmount No.{key}
          </button>
        ))}
      </div>
      {editorKeys.map((key) => (
        <div key={key} className="h-32">
          <EditorComponent
            placeholder={`Editor No.${key} of ${editorKeys.length}`}
          />
        </div>
      ))}
    </div>
  )
}

export default EditorGroup

extension-component.tsx

import { definePlaceholder } from 'prosekit/extensions/placeholder'
import { useExtension } from 'prosekit/react'
import { useMemo } from 'react'

export default function ExtensionComponent({
  placeholder,
}: {
  placeholder: string
}) {
  const extension = useMemo(
    () => definePlaceholder({ placeholder }),
    [placeholder],
  )

  useExtension(extension)

  return null
}