code: function buildUrl(urlPattern, customParams) {
      var url = formatUrl.apply(null, urlPattern);
  
      url = appendParams(url, customParams);
      return url;
    }
docs: Just helper funckion to build the request URL.
  
  @param {array<string>} urlPattern array in format of [urlFormat, arg1, arg2] used to build the URL.
  @param {object} customParams key/value pair of params.
  @returns {string} the URL built.