生成uuid

        function uuid (hasHyphen) {
  return (hasHyphen ? 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx' : 'xxxxxxxxxxxx4xxxyxxxxxxxxxxxxxxx').replace(/[xy]/g, function (c) {
        const r = Math.random() * 16 | 0
        const v = c == 'x' ? r : (r & 0x3 | 0x8)
        return v.toString(16)
  })
}