XMLHttpRequest Object

Hi,

The below code works on IE, Chrome etc but not with safari, 

function Add_PRD()
{

if (window.XMLHttpRequest) { u = new XMLHttpRequest;} else { u = new ActiveXObject("Microsoft.XMLHTTP"); }

u.onreadystatechange = function () {
if (u.readyState == 4 && u.status == 200) { Assign_Values1(u.responseText); }
}; u.open("GET", "Add_Product.aspx?Prd_ID=10", true);

u.send();return false;
}

Please advise why this doesn't work with Safari?