Laravel AJAX POST request is empty

Question

When I pass POST data through AJAX to my controller it is empty. In the AJAX the data is still there but after I send it the controller it says it is empty.

AJAX:

  function usernameCheck()
{
    var input = document.getElementById("usernameInput");
    var icon = document.getElementById("userIcon");
    var xmlhttp,
        username = document.getElementById("usernameInput"),
        message = document.getElementById("usernameMessage");

    if (username.value != "") {
        if (window.XMLHttpRequest) {
           // code for IE7+, Firefox, Chrome, Opera, Safari
           xmlhttp=new XMLHttpRequest();
        } else {
            // code for IE6, IE5
            xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
        }
        xmlhttp.onreadystatechange = function() {
            if (xmlhttp.readyState==4 && xmlhttp.status==200) {

                // FOR DEBUGGING
                console.log(xmlhttp.responseText);

            }
        }
    }

    xmlhttp.open("POST", "usernamevalidation", true);
    xmlhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
    xmlhttp.send("username=" + username.value);
    }
  }

Routes.php:

Route::post('usernamevalidation', 'UserController@validateUsername');

UserController.php:

class UserController extends BaseController {

    public function validateUsername() {

       // FOR DEBUGGING
       dd(Input::all());

    }
}

The code that I console.logged (which is empty and should contain the username):

<pre class='xdebug-var-dump' dir='ltr'>
<b>array</b> <i>(size=0)</i>
  <i><font color='#888a85'>empty</font></i>
</pre>

Answer 1

In the awareness that I'm giving my answer here one year later since the last comment, I've stumbled on the some error using Laravel 5.2 and working with XMLHttpRequest objects: finally I ended to analyze and compare post request headers, which led me to simply setting both:

xmlhttp.setRequestHeader('X-Requested-With', 'XMLHttpRequest');
xmlhttp.setRequestHeader('Content-type', 'application/x-www-form-urlencoded; charset=UTF-8');

That solved my empty responseText. Hope this can help someone else or can be used for future reference.