code: function writeFileAsync (filename, content, options, cb) {
    if (typeof filename !== 'string') {
      throw new Error('path must be a string')
    }
  
    if (typeof options === 'function') {
      cb = options
    }
  
    mkdirp(path.dirname(filename), function (err) {
      if (err && typeof cb === 'function') {
        return cb(err)
      }
  
      fs.writeFile(filename, content, options, cb)
    })
  }
docs: Asynchronous write