IE11 not honoring responseType: 'json'

I am trying to execute a simple xhr.get call and use the json object in response.body. This works fine in Chrome and Firefox, but in IE11; it does not convert the response.body into an object, but leaves it as a String. Here it only converts the response.body if isJson is set in the options ahead of time. I have no need for that property besides to hack it to work for IE11. Shouldn’t isJson be set to true if the responseType is ‘json’ or the json property exists?

Returns a string in response.body in IE11

xhr.get({
  url: myUrl?parameters,
  responseType: 'json'
}, callback);

My hack to convert response.body to an Object in IE11

xhr.get({
  url: myUrl?parameters,
  responseType: 'json',
  json: true
}, callback);

It looks like Microsoft is aware of it, but no fix coming for IE11.

[stloc]

on IE don’t use xhr.responseType = 'json'; and parse yourself the response var res = JSON.parse(xhr.responseText);

var xhr = new XMLHttpRequest();
    //xhr.responseType = 'json';
    var params = ...
    xhr.open("POST", "/xxx", true);
    xhr.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
    xhr.onreadystatechange = function() {//Call a function when the state changes.
      if(xhr.readyState == 4 && xhr.status == 200) {
        var res = JSON.parse(xhr.responseText);
      }
    }
    xhr.send(params);

[TehShrike]

It has seemed pretty odd to me that you have to specify json: true even when the server is putting Content-Type:application/json headers on the response.