panel/app/javascript/packs/serializer.js

// From https://raw.githubusercontent.com/ProseMirror/prosemirror-markdown/master/src/to_markdown.js
import { MarkdownSerializer } from 'prosemirror-markdown'

export default new MarkdownSerializer(
  {
    blockquote(state, node) {
      state.wrapBlock('> ', null, node, () => state.renderContent(node))
    },
    code_block(state, node) {
      state.write('```' + (node.attrs.params || '') + '\n')
      state.text(node.textContent, false)
      state.ensureNewLine()
      state.write('```')
      state.closeBlock(node)
    },
    heading(state, node) {
      state.write(state.repeat('#', node.attrs.level) + ' ')
      state.renderInline(node)
      state.closeBlock(node)
    },
    horizontal_rule(state, node) {
      state.write(node.attrs.markup || '---')
      state.closeBlock(node)
    },
    bullet_list(state, node) {
      state.renderList(node, '  ', () => (node.attrs.bullet || '*') + ' ')
    },
    ordered_list(state, node) {
      let start = node.attrs.order || 1
      let maxW = String(start + node.childCount - 1).length
      let space = state.repeat(' ', maxW + 2)
      state.renderList(node, space, i => {
        let nStr = String(start + i)
        return state.repeat(' ', maxW - nStr.length) + nStr + '. '
      })
    },
    list_item(state, node) {
      state.renderContent(node)
    },
    paragraph(state, node) {
      state.renderInline(node)
      state.closeBlock(node)
    },

    image(state, node) {
      state.write(
        '![' +
          state.esc(node.attrs.alt || '') +
          '](' +
          state.esc(node.attrs.src) +
          (node.attrs.title ? ' ' + state.quote(node.attrs.title) : '') +
          ')',
      )
    },
    hard_break(state, node, parent, index) {
      for (let i = index + 1; i < parent.childCount; i++)
        if (parent.child(i).type != node.type) {
          state.write('\\\n')
          return
        }
    },
    text(state, node) {
      state.text(node.text)
    },
  },
  {
    em: {
      open: '*',
      close: '*',
      mixable: true,
      expelEnclosingWhitespace: true,
    },
    strong: {
      open: '**',
      close: '**',
      mixable: true,
      expelEnclosingWhitespace: true,
    },
    mark: {
      open: '==',
      close: '==',
      mixable: true,
      expelEnclosingWhitespace: true,
    },
    strikethrough: {
      open: '~~',
      close: '~~',
      mixable: true,
      expelEnclosingWhitespace: true,
    },
    link: {
      open(_state, mark, parent, index) {
        return isPlainURL(mark, parent, index, 1) ? '<' : '['
      },
      close(state, mark, parent, index) {
        return isPlainURL(mark, parent, index, -1)
          ? '>'
          : '](' +
              state.esc(mark.attrs.href) +
              (mark.attrs.title ? ' ' + state.quote(mark.attrs.title) : '') +
              ')'
      },
    },
    code: {
      open(_state, _mark, parent, index) {
        return backticksFor(parent.child(index), -1)
      },
      close(_state, _mark, parent, index) {
        return backticksFor(parent.child(index - 1), 1)
      },
      escape: false,
    },
  },
)