为什么服务器响应失败并无法加载资源：服务器响应状态为500（内部服务器错误）？我该如何解决？

我想在Ajax中传递数据，但是在运行该功能时，当我检查该元素时会出现“内部服务器错误”。我正在建立一个登录表单，但是当单击登录按钮时，它会出现内部服务器错误。

 function login (){

var xhttp = new XMLHttpRequest(); xhttp.onreadystatechange = function() { if (this.readyState == 4 && this.status == 200) { console.log("Test2"); document.getElementById("IdForm").innerHTMl = this.responseText; console.log("Test3"); alert (this.responseText); } };

xhttp.open("POST", "PHP/login.php", true); var data = new FormData(document.getElementById("IdForm")) console.log("Status500") xhttp.send(data);

return false; } 我在这里您有PHP代码：

 <?php
  $servername = "localhost";
  $username = "*****";
  $password = "******";
  $dbname = "*******";
  //create connection
  $conn = new mysqli ($servername, $username, $password, $dbname);
 //Check connection

 if ($conn ->connect_error) 
 {
 die("connection failed:" . $conn -> connect_error);
  }
 $sql = "SELECT * FROM accounts";
 $result = $conn ->query($sql);
 $out = "";
 $rc = "";
 if ($result->num_rows > 0)
 {
while($row = $result -> fetch_assoc())
 {

echo "<p> " . $_POST ["username"] . "</p>";
if (($row ["username"] == $_POST ["username"]) and $row ["password"] == $_POST ["password"])
header('Location: ok.html');
else
echo "User not valid";
 }
 } else{
echo "0 results";
 }
 */
  ?>

问题来源于stack overflow