function save()
{

    var hist = document.getElementById("hist").value;
                var mission =   document.getElementById("mission").value;

            var params = "history=" + hist+ "&mission=" + mission;
 var xmlhttp = new XMLHttpRequest();
        xmlhttp.onreadystatechange = function()
        {
             if (this.readyState == 4 && this.status == 200 )
            {

                 UserAccountInfo =   this.responseText;
                 alert(UserAccountInfo);
            }
        }
        xmlhttp.open("POST","savecompany.php",true);
        xmlhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
        xmlhttp.send(params);
}

<?php

    require "conn.php";


    $history= $_POST["history"];
    $mission = $_POST["mission"];

    $sql = " UPDATE company SET history ='$history' , mission='$mission'  where id='1'";
    mysqli_query($conn,$sql);


echo "done";
mysqli_close($conn);
?>