PHP develops simple book background management system password change function

We completed the administrator password modification page in the previous section

This section will implement this function

<script type="text/javascript">
  function checkspace(checkstr) {
    var str = '';
    for(i = 0; i < checkstr.length; i++) {
      str = str + ' ';
    }
    return (str == checkstr);
  }
  function check()
  {
    if(checkspace(document.renpassword.password.value)) {
      document.renpassword.password.focus();
      alert("原密码不能为空！");
      return false;
    }
    if(checkspace(document.renpassword.password1.value)) {
      document.renpassword.password1.focus();
      alert("新密码不能为空！");
      return false;
    }
    if(checkspace(document.renpassword.password2.value)) {
      document.renpassword.password2.focus();
      alert("确认密码不能为空！");
      return false;
    }
    if(document.renpassword.password1.value != document.renpassword.password2.value) {
      document.renpassword.password1.focus();
      document.renpassword.password1.value = '';
      document.renpassword.password2.value = '';
      alert("新密码和确认密码不相同，请重新输入");
      return false;
    }
    document.admininfo.submit();
  }
</script>

<?php
$password=$_SESSION["pwd"];
$sql="select * from admin where password='$password'";
$rs=mysqli_query($link,$sql);
$rows=mysqli_fetch_assoc($rs);
$submit = isset($_POST["Submit"])?$_POST["Submit"]:"";
if($submit)
{
  if($rows["password"]==$_POST["password"])
  {
    $password2=$_POST["password2"];
    $sql="update admin set password='$password2' where id=1";
    mysqli_query($link,$sql);
    echo "<script>alert('修改成功,请重新进行登陆！');window.location='login.php'</script>";
    exit();
  }
  else
    ?>
    <?php
  {
    ?>
    <script>
      alert("原始密码不正确,请重新输入")
      location.href="renpassword.php";
    </script>
    <?php
  }
}
?>