<?php
$email=$_POST['email'];
$password=md5$_POST['password'];

$result = mysqli_query($con, "SELECT * FROM User WHERE email= '$email' AND password = '$password'");
//var_dump($result);

$count = mysqli_num_rows($result);
//var_dump($count);

  if($count == 1)
  {
    echo ("Exists");
  }
  else
  {
    echo ("Error");
  }

?>

$(document).ready(function() {
  $("#submit").click(function() {

    var email = document.getElementById("email").value;
    var password = document.getElementById("password").value;

    var xhttp = new XMLHttpRequest();
    xhttp.onreadystatechange = function()
    {
       if(this.readyState == 4 && this.status == 200)
       {
        var response = this.responseText;

        if(response == "Exists")
        {
          window.location="content.html"
        }

        else if(response == "Error")
        {
          alert("Wrong email or password");
        }
  }
}
xhttp.open("POST", "checkDetails.php", true);
xhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
xhttp.send("email="+email+"password="+password);
        return false;
      });
});