How to use the prosemirror-model.Node.prototype function in prosemirror-model

function flatten(schema, children, f) {
  let result = [], pos = 0, tag = noTag

  for (let i = 0; i < children.length; i++) {
    let child = children[i]
    if (child.tag && child.tag != Node.prototype.tag) {
      if (tag == noTag) tag = Object.create(null)
      for (let id in child.tag)
        tag[id] = child.tag[id] + (child.flat || child.isText ? 0 : 1) + pos
    }

    if (typeof child == "string") {
      let re = /<(\w+)>/g, m, at = 0, out = ""
      while (m = re.exec(child)) {
        out += child.slice(at, m.index)
        pos += m.index - at
        at = m.index + m[0].length
        if (tag == noTag) tag = Object.create(null)
        tag[m[1]] = pos
      }
      out += child.slice(at)
      pos += child.length - at

import {Node} from "prosemirror-model"

const noTag = Node.prototype.tag = Object.create(null)

function flatten(schema, children, f) {
  let result = [], pos = 0, tag = noTag

  for (let i = 0; i < children.length; i++) {
    let child = children[i]
    if (child.tag && child.tag != Node.prototype.tag) {
      if (tag == noTag) tag = Object.create(null)
      for (let id in child.tag)
        tag[id] = child.tag[id] + (child.flat || child.isText ? 0 : 1) + pos
    }

    if (typeof child == "string") {
      let re = /<(\w+)>/g, m, at = 0, out = ""
      while (m = re.exec(child)) {
        out += child.slice(at, m.index)