function ajax_runs3(value){
var ajaxRequest;  // The variable that makes Ajax possible!
    try{
        ajaxRequest = new XMLHttpRequest();
    } catch (e){
        // Internet Explorer Browsers
        try{
            ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
        } catch (e) {
            try{
                ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
            } catch (e){
                // Something went wrong
                alert("Your browser broke!");
                return false;
            }
        }
    }
    ajaxRequest.onreadystatechange = function(){
        if(ajaxRequest.readyState == 4){
            document.myForm.time.value = ajaxRequest.responseText;
        }
    }

    var runs3= value;
    ajaxRequest.open("POST","runs3.php"+ runs3, true);
    ajaxRequest.send(null);
}

<?php
$servername = "localhost";
$username = "labi8575_admin";
$password = "ParAnoikOs13";
$dbname = "labi8575_inventory";
$conn = mysql_connect($servername, $username, $password);
if(! $conn )
{
  die('Could not connect: ' . mysql_error());
}
mysql_select_db('labi8575_inventory');
$runs3 = $_POST["runs3"];
$sql = mysql_query("UPDATE demo SET runs3 = '$runs3'");
$retval = mysqli_query( $sql, $conn );
?>