getJSON.js

var getJSON = function(url, callback) {
    var xhr = new XMLHttpRequest();
    xhr.open("get", url, true);
    xhr.responseType = "json";
    xhr.onload = function() {
      var status = xhr.status;
      if (status == 200) {
        callback(null, xhr.response);
      } else {
        callback(status);
      }
    };
    xhr.send();
};