筆記一下，怕忘記

亂數取 Array 內的任一值

var portList = ['6001', '6002', '6003', '6004', '6005', '6006', '6007', '6008'];
portList.getRandom = function () {
  return this[Math.floor(Math.random() * this.length)];
};
var port = portList.getRandom();