need to pass variable to function

I am trying to pass a variable to a a function that I believe calls another function (I think) but am having problems. The variable I need to use in the second function is productid but several ways thAt I have tried have not worked. either a fix in javascript or Jquery will be great!!!

This is the line that I need the variable for

var error_url = '/ProductDetails.asp?ProductCode'  + productid;

this is where the variable originates from...

var productid = form.elements['ProductCode'].value;

and here is the whole js code

function addToCart2(form, button) {
var softAdd = true;
var productid = form.elements['ProductCode'].value;

      var qstr;
  var bttnName = button.name;
    button.disabled = true;
    if (form.elements['ReturnTo']) {
        form.elements['ReturnTo'].value = "";
    }
    qstr = serialize(form, bttnName + '.x', '5', bttnName + '.y', '5');
            sendAjax('POST','/ProductDetails.asp?ProductCode=' + productid  + '&AjaxError=Y', qstr , retrieveProductError2 ,displayServerError,false);
    button.disabled = false;
            return false;
        }
function retrieveProductError2(result, statusCode) {
var ele = document.getElementById('listOfErrorsSpan');
var errorIndex = result.indexOf('<carterror>');
var productIndex = result.indexOf('<ProductIndex>')
if (errorIndex > -1 && productIndex == -1)  {
var error_url = '/ProductDetails.asp?ProductCode'  + productid;
window.location = error_url;
} 
if (errorIndex != -1) {
    //ele.innerHTML = result.slice(errorIndex + 11, result.indexOf('</carterror>'));
}
else {
    ele.innerHTML = "";
    if (productIndex == -1) {
    sendAjax('GET','/AjaxCart.asp?GetIndex=True', '', showCart, null, false);
    }
    else {
    productIndex = result.slice(productIndex + 14, result.indexOf('</ProductIndex>'));
    sendAjax('GET','/AjaxCart.asp?Index=' + productIndex, '', showCart, null, false);
    }
}

}

The easiest way is to just move your variable declaration outside of your method. So change the declaration of product id outside your addToCart2 method. So outside of that method you do this:

var product_id;

Then inside your method remove var from product_id and it will just be an assignment and not declaration.

Where you pass in retrieveProductError2 as your error callback for the sendAjax call, you could instead pass in:

function(result, statusCode) { retreiveProductError2(result, statusCode, productId);}

Then change the definition of your retreiveProductError2 function to accept the additional parameter.