Node / Express parsed JSON POST is not valid JSON - json

Question

I am making a JSON POST request using Pure Javascript XMLHttpRequest, however Express appears to wrap the received JSON in an additional object, how can I prevent this ?
I am using the bodyParser:
app.use(bodyParser.json({limit: '50mb'}));
This is the client sending the JSON data:
var xhr = new XMLHttpRequest();
xhr.open("POST", "https://xxx.my.net/",true);
// This header MUST be present for POST requests.
xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
xhr.setRequestHeader("Accept", "application/json, text/javascript");
xhr.send(JSON.stringify({"hxx":1}));
And this is Nodejs / Express middleware:
app.use(function(req, res, next){
fn.console.log(req.body);
})
This is the console.log output:
{ '{"hxx":1}': '' }
I know that I can parse the body with:
console.log(JSON.parse(Object.keys(req.body)[0]))
but I would prefer not to have to do this !
IMPORTANT Note
I have already tried using content type = "application/json" but when I do this the request becomes a GET instead of a POST, and Unless I state "application/x-www-form-urlencoded" the request is automatically converted by the browser from a POST to a GET.