Hỏi về truyền masp mà không cần dùng a href

<a onclick="javascript:addbasket('masp')">thêm vào giỏ hàng</a>

function addbasket(masp)
{
      var http_request = false;
      if (window.XMLHttpRequest) { // Mozilla, Safari,...
         http_request = new XMLHttpRequest();
         if (http_request.overrideMimeType) {
         	// set type accordingly to anticipated content type
            //http_request.overrideMimeType('text/xml');
            http_request.overrideMimeType('text/html');
         }
      } else if (window.ActiveXObject) { // IE
         try {
            http_request = new ActiveXObject("Msxml2.XMLHTTP");
         } catch (e) {
            try {
               http_request = new ActiveXObject("Microsoft.XMLHTTP");
            } catch (e) {}
         }
      }
      if (!http_request) {
         alert('Cannot create XMLHTTP instance');
         return false;
      }

      http_request.onreadystatechange = function(){
      if (http_request.readyState == 4) {
         if (http_request.status == 200) {
             var result=http_request.responseText;
             if ((result!="")&&(callback!="")){

                //kết quả trả về trong biến result
                // tùy vào kết quả mà xử lý
                
             }
         } else {
            alert('There was a problem with the request.');
         }
      }
      };
      var parameters="masp="+masp; 
      http_request.open('POST', 'add_product.aspx', true);
      http_request.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
      http_request.setRequestHeader("Content-length", parameters.length);
      http_request.setRequestHeader("Connection", "close");
      http_request.send(parameters);
}