XMLhttprequest.send() doesn't send variables to PHP

Question

I have this code.

JAVASCRIPT

function removeAndReplace(id, sezione){
   var xhttp = new XMLHttpRequest();

   xhttp.onreadystatechange = function() {
      if (xhttp.readyState == 4 && xhttp.status == 200) {
         alert(xhttp.responseText);
      }
   }

   xhttp.open("POST", "removeAndReplace.php", true);
   xhttp.send("id=" + id + "&sezione=" + sezione);
}

PHP

 print_r($_POST);

 $id = $_POST['id'];
 $sezione = $_POST['sezione'];
 .
 .
 .

HTML

<input type="button" value="Elimina" class="btn_elimina" onClick="removeAndReplace(1, 'Shopping')">

I want to call a PHP function after the button click so I read that the better way is to use AJAX.

Firefox and Chrome return this error message:

Array ( )
Notice: Undefined index: id in C:\pweb\tools\xampp\htdocs\Bazaar\php\removeAndReplace.php on line 6

Notice: Undefined index: sezione in C:\pweb\tools\xampp\htdocs\Bazaar\php\removeAndReplace.php on line 7

Line 6 is: $id = $_POST['id']; Line 7 is: $sezione = $_POST['sezione'];

Where am I going wrong?

Can you add a little more detail about how the function is called? Perhaps show the HTML? — Professor Abronsius
– Professor Abronsius, Commented Jun 23, 2017 at 8:29

Quentin · Accepted Answer · 2017-06-23 14:32:24Z

You are dumping your data into the request body without telling the server how it is formatted.

Since PHP doesn't know you have sent it data in an encoding it understands, it ignores the request body.

You need to add:

xhttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");

… before you send the request.

Aside

While your hard coded data is free of special characters, it is best practice to encode your data. This will save you headaches in the future:

xhttp.send("id=" + encodeURIComponent(id) + "&sezione=" + encodeURIComponent(sezione));

You can save yourself the trouble of manually encoding the data and having to set your own content-type by using the FormData API:

var data = new FormData();
data.append("id", id);
data.append("sezione", sezione);

xhttp.open("POST", "removeAndReplace.php", true);
xhttp.send(data);

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