HTML5 Game - Use XMLHttpRequest to read value from php

Description

Use XMLHttpRequest to read value from php

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>Ask The Server</title>
  <style>
body {
  font-family: Verdana;
  font-size: 12px;
}

div {
  margin: 20px;
  border: black 1px solid;
  padding: 10px;
  background-color: #FBF3CB;
}

input {
  width: 75px;
}

#result {
  color: darkred;
  font-weight: bold;
}
  </style>
  <script>
  let req = new XMLHttpRequest();

function askServer() {

  let number1 = document.getElementById("number1").value;
  let number2 = document.getElementById("number2").value;

  let dataToSend = "?number1=" + number1 + "&number2=" + number2;
  req.open("GET", "WebCalculator.php" + dataToSend, true);
  req.onreadystatechange = handleServerResponse;
  req.send();

  document.getElementById("result").innerHTML = "The request has been sent.";
}


function handleServerResponse() {
  if ((req.readyState == 4) && (req.status == 200))
 {
    let result = 
req.responseText;
    document.getElementById("result").innerHTML = "The answer is: " + result;
  }
}

  </script>
</head>

<body>
<div>
  <p>Enter two numbers:
    <input id="number1" type="number">
    <input id="number2" type="number">
  </p>
  <p>To ask the server to add them, without refreshing the page, click
this button:
    <button onclick="askServer()">Ask the Server</button>
  </p>
</div>
  <p id="result"></p>
</body>
</html>

WebCalculator.php

<?php
       $num1 = $_GET['number1'];
       $num2 = $_GET['number2'];
echo ($num1 + $num2); 

?>