AddCartItem.ss

function service(request,response)
{
  var itemid = request.getParameter('itemid');
  var qty = request.getParameter('quantity');
 
  // create a plain object for the itme
  var item = {internalid : itemid, quantity: qty}
 
  // Get a reference to the shopping order
  var order = nlapiGetWebContainer().getShoppingSession().getOrder();
 
  // Add the item to cart
  try
  {
    var returnval = order.addItem(item);
 
    response.writeLine(JSON.stringify(returnval));
  }
  catch (e)
  {
    var e2 = nlapiCreateError(e);
    // Do error handling here
  }
 
}