https://faq.whatsapp.com/en/android/26000002/

vue-whatsapp-formatting.js

const components = {
  '*': 'strong',
  '_': 'em',
  '~': 's',
  '```': 'code'
}

export default {
  functional: true,
  props: {
    tag: {
      default: 'span'
    },
    recursive: {
      type: Boolean,
      default: false
    }
  },
  render (h, context) {
    const { recursive } = context.props

    function parse (markdown) {
      const re = new RegExp('(\\*|_|~|```)([^\\1]*?)\\1', 'g')
      const vnodes = []
      let lastIndex = 0
      let match

      while ((match = re.exec(markdown)) !== null) {
        const [, char, text] = match
        const tag = components[char]
        const child = tag ? h(tag, recursive ? parse(text) : text) : text
        vnodes.push(markdown.slice(lastIndex, match.index), child)
        lastIndex = re.lastIndex
      }

      return vnodes.concat(markdown.slice(lastIndex))
    }

    const [vnode] = context.slots().default
    return h(context.props.tag, parse(vnode.text))
  }
}