testXhrType = function(type) {
    if (typeof XMLHttpRequest === 'undefined') {
      return false;
    }
    var xhr = new XMLHttpRequest();
    xhr.open('get', '/', true);
    try {
      xhr.responseType = type;
    } catch (error) {
      return false;
    }
    return 'response' in xhr && xhr.responseType === type;
  }
https://mathiasbynens.be/notes/xhr-responsetype-json#comment-4

@author Mathias Bynens
@access private
@function testXhrType
@param {string} type - String name of the XHR type you want to detect
@returns {boolean} true if the responseType is of the specified type