// ArrayBuffer转16进度字符串示例
function ab2hex(buffer) {
  var hexArr = Array.prototype.map.call(
    new Uint8Array(buffer),
    function(bit) {
      return ('00' + bit.toString(16)).slice(-2)
    }
  )
  return hexArr.join('');
}
wx.onBluetoothDeviceFound(function(res) {
  var devices = res.devices;
  console.log('new device list has founded')
  console.dir(devices)
  console.log(ab2hex(devices[0].advertisData))
})
z这个函数有时候会报错，这事api给的实例，看log是初始化Uint8Array时，buffer的长度无效，
错误如下：
Invalid array length argument;at onBluetoothDeviceFound callback function
Uint8Array@[native code]
ab2hex@https://usr/app-service.js:1076:609