代码如下所示：

<script>  
  function password() {undefined
  var testV = 1;
  var mm = prompt('请输入密码','');
  while (testV < 300) {undefined
  if (!mm)
  history.go(-1);
  if (mm == "666666") {//初始密码
  break;
  }
  testV+=1;
  var mm =
  prompt('密码错误!请重新输入:');
  }
  if (mm!="password" & testV ==3)
  history.go(-1);
  return " ";
  }
  document.write(password());  
</script>
<script>  
  function password() {undefined
  var testV = 1;
  var mm = prompt('请输入密码','');
  while (testV < 300) {undefined
  if (!mm)
  history.go(-1);
  if (mm == "666666") {//初始密码
  break;
  }


  testV+=1;
  var mm =
  prompt('密码错误!请重新输入:');
  }
  if (mm!="password" & testV ==3)
  history.go(-1);
  return " ";
  }
  document.write(password());  
</script>
<script>  
  function password() {undefined
  var testV = 1;
  var mm = prompt('请输入密码','');
  while (testV < 300) {undefined
  if (!mm)
  history.go(-1);
  if (mm == "666666") {//初始密码
  break;
  }


  testV+=1;
  var mm =
  prompt('密码错误!请重新输入:');
  }
  if (mm!="password" & testV ==3)
  history.go(-1);
  return " ";
  }
  document.write(password());  
</script>