JSON.parse is not working - ajax

Question

I'm having a very strange problem. My JSON.parse does not seem to work. I tried using eval too but that didn't help either. Below is my code:
var responseDoc = xmlHttp.responseText;
document.getElementById("debug1").innerHTML=responseDoc;
var response = JSON.parse(responseDoc);
document.getElementById("debug2").innerHTML=response.category;
My responseDoc looks like this
{"id":null,"category":"dog","price":"4321","name":"new product 123","sku":"1234","success":true}
But response.category is "undefined". Any ideas why this is happening? I've spent hours on it but couldn't figure out. Thanks a lot!
*UPDATE*:
Removed stringify as some people suggested -> still not working.
If I tried the code below, I get "Uncaught SyntaxError: Unexpected token <" from the console:
var response = JSON.parse(xmlHttp.responseText);
*UPDATE 2 *:
Found the problem. It's because my responseDoc is getting an HTML Doc. Not a JSON Object. Not sure why that happens. This is the code where I process ajax request (I'm using jsp):
JSONObject result = new JSONObject();
result.put("success",true);
result.put("id",request.getParameter("id"));
result.put("name", request.getParameter("name"));
result.put("sku",request.getParameter("sku"));
result.put("price",request.getParameter("price"));
result.put("category",request.getParameter("category"));
out.print(result);
out.flush();

Answer 1

You don't need to stringify something that is already a string (xmlHttp.responseText). The stringify method should be used on a javascript object to serialize it into a JSON string. So get rid of this stringification and simply parse the JSON string that you already have (using the JSON.parse method):
var response = JSON.parse(responseDoc);

Answer 2

You don't need to stringify a string :
var response = JSON.parse(responseDoc);