Getting the most basic ajax working on xampp on windows 7 to check for internet connectivity

Question

Before submitting a form onclick="return check_internet_conn()" is called to see if there is an internet connection, (I will be doing this on a mobile device, xampp will be on mobile device too. My testing happens on windows 7), this will request check_internet_connection.php file to check internet connection (prefer not to check to see if an image exists on some server to check for internet connectivity via javascript). check_internet_connection.php works fine but I can never get javascript ajax, jQuery ajax, nor javascript fetch(), return the file content.

<div class="container">
  <form action="processQuestion.php" method="post">
   <div class="form-group">
     <label for="question">Write your question here:</label>
     <textarea class="form-control" rows="7" id="question_txt" name="question"></textarea>
   </div>
   <button type="submit" class="btn btn-primary" onclick="return check_internet_conn()">Submit Question</button> 
  </form>
  <p id="submit_error_no_internet" class="warning"></p>
</div>

Here is the PHP file

<?PHP

try {
@   $connected = fsockopen("www.example.com", 80);
    if ($connected) {
        fclose($connected);
        echo "Connected";
    }
}   

catch(Exception $e) {
  echo 'Message: ' .$e->getMessage();
}

finally {
  echo "Not Connected!";
}

?>

And here are the three different attempts at ajax and js fetch(), with debugging additions.

<script src="jquery/jquery-3.5.1.slim.min.js"></script>
<script src="bootstrap-4.5.3-dist/js/bootstrap.bundle.min.js"></script>
<script>

function check_internet_conn() {
    $.get("http://localhost/crud/check_internet_connection.php", function(data, status){
            switch(data) {
            case "Not Connected!":
                document.getElementById("submit_error_no_internet").innerHTML = "No Internet connection, connect to internet.";
                return false;
                break;
            case "ConnectedNot Connected!":
                return true;
                break;
            default:
                document.getElementById("submit_error_no_internet").innerHTML = "Nothing works";
            } 
        });
}

function check_internet_conn() {

    async function getText(file) {
        let myObject = await fetch(file);
        let myText = await myObject.text();
        switch(myText) {
        case "Not Connected!":
            document.getElementById("submit_error_no_internet").innerHTML = "No Internet connection, connect to internet.";
            return false;
            break;
        case "ConnectedNot Connected!":
            return true;
            break;
        default:
            document.getElementById("submit_error_no_internet").innerHTML = "Nothing works";
        }
    }

  getText("http://localhost/crud/check_internet_connection.php");
  
}


function check_internet_conn() {

    var myXmlhttp = new XMLHttpRequest();
    myXmlhttp.onreadystatechange = function() {
      if (this.readyState == 4 && this.status == 200) {
        document.getElementById("submit_error_no_internet").innerHTML = this.responseText;
        switch(this.responseText) {
            case "Not Connected!":
                document.getElementById("submit_error_no_internet").innerHTML = "No Internet connection, connect to internet.";
                return false;
                break;
            case "ConnectedNot Connected!":
                return true;
                break;
            default:
                document.getElementById("submit_error_no_internet").innerHTML = "Nothing works";
        } 
      }
    };
    myXmlhttp.open("GET", "http://localhost/crud/check_internet_connection.php");
    myXmlhttp.send();
    document.getElementById("submit_error_no_internet").innerHTML = myXmlhttp.status + " " + myXmlhttp.readyState;
}

</script>

I have attempted debugging in Firefox and Chrome, without much success. No error messages.

Answer 1

I would do something like:

<button onclick="checkConnection()">Check connection</button>

function checkConnection() {
$(document).ready(function() {
  $.ajax({
      url: "yourUrl",
      success: function(result) {
          if(result) {
          // you are connected
          } else {
          // you are not connected
          }
      },
      error: function(error) {
          // do something sad
      }
  });
});

function is_connected() {
$connected = @fsockopen("www.example.com", 80); 
if ($connected){
    $is_conn = true; //action when connected
    fclose($connected);
}else{
    $is_conn = false; //action in connection failure
}
echo($is_conn);
die();
}