为什么此代码在我有一个输出时在警报字段中显示两个结果？

switch (new Date().getDay()) {
  case 0:
    {
      alert("sunday");
    }
  case 1:
    {
      alert("monday");
      break;
    }
  case 2:
    {
      alert("tueseday");
      break;
    }
  case 3:
    {
      alert("wednesday");
      break;
    }
  case 4:
    {
      alert("thursday");
      break;
    }
  case 5:
    {
      alert("friday");
      break;
    }
  case 6:
    {
      alert("saturday");
      break;
    }
}