Marked custom extension not working

marked.js

import marked from 'marked'

const variable = {

  name: 'variable',
  level: 'block',
  start (src) { return src.match(/\{{(.*?)}}/g)?.index },
  tokenizer (src, tokens) {
    const rule = /\{{(.*?)}}/g
    const match = rule.exec(src)
    if (match) {
      return {
        type: 'variable', // Should match "name" above
        raw: match[0], // Text to consume from the source
        variable: this.inlineTokens(match[1].trim())
      }
    }
  },
  renderer (token) {
    return `\n<span class="variable">${this.parseInline(token.variable)}</span>`
  }
}
marked.use({ extensions: [variable] })

export function markdownToHTML (str) {
  if (!str) {
    return ''
  }
  return marked(str)
}