code: function (url, key, value) {
                  var regex = new RegExp("([?|&])" + key + "=.*?(&|#|$)(.*)", "gi"),
                      separator,
                      hash;
  
                  if (regex.test(url)) {
                      url = url.replace(regex, '$1' + key + "=" + value + '$2$3');
                  } else {
                      separator = url.indexOf('?') !== -1 ? '&' : '?';
                      hash = url.split('#');
                      url = hash[0] + separator + key + '=' + value;
                  }
                  return url;
              }
docs: Appends the callback parameter to the existing url
  @param {string} url
  @param {string} key
  @param {string} value
  @returns {string}