How To Return xmlHttp request status?

I would like to know how to verify the status of an xmlHttp request after sending it. How do I go about doing it? Thanks.

function sendRequest(){
    //get refresh access token   
    var accessToken = 'xxx';
    //get user_id
    var userid = document.getElementById('userid').value;
    //get request_token
    var requestToken = document.getElementById('requestToken').value;

     //insert database
     var xmlHttp = new XMLHttpRequest();
     var url="database.php";
     var parameters = "accessToken=" + accessToken + "&userid=" + userid + "&requestToken=" + requestToken ;
     xmlHttp.open("POST", url, true);

    //send request
     xmlHttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
     xmlHttp.setRequestHeader("Content-length", parameters.length);
     xmlHttp.setRequestHeader("Connection", "close");
     xmlHttp.send(parameters);

    //check status
    if(xmlHttp.status == Ok){
        alert('success!');
    }else {
        alert('error');
    }

}

Solution

<!DOCTYPE html>
<html>
<body>

<h2>Using the XMLHttpRequest object</h2>

<button type="button" onclick="loadXMLDoc()">Change Content</button>

<p id="test"></p>

<script>


function sendRequest(){
    //get refresh access token   
    var accessToken = 'xxx';
    //get user_id
    var userid = document.getElementById('userid').value;
    //get request_token
    var requestToken = document.getElementById('requestToken').value;


    var xmlHttp = new XMLHttpRequest();
    var xhttp = new XMLHttpRequest();
    xmlHttp.onreadystatechange = function() {
      if (this.readyState == 4 && this.status == 200) {
        document.getElementById("test").innerHTML =
        this.responseText;
      }
    };
    //insert database
     var url="database.php";
     var parameters = "accessToken=" + accessToken + "&userid=" + userid + "&requestToken=" + requestToken ;
     xmlHttp.open("POST", url, true);

    //send request
     xmlHttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
     xmlHttp.setRequestHeader("Content-length", parameters.length);
     xmlHttp.setRequestHeader("Connection", "close");
     xmlHttp.send(parameters);



}

</script>

</body>
</html>