code: function (payload, callback) {
                  var args = {},
                      argsKeys = ['location', 'page', 'title'];
  
                  argsKeys.forEach(function consumer(prop) {
                      if (payload.hasOwnProperty(prop)) {
                          args[prop] = payload[prop];
                      }
                  });
  
                  args.hitCallback = callback;
                  // `page` is alias to `url`
                  if (payload.hasOwnProperty('url')) {
                      args.page = payload.url
                  }
  
                  _command.call(this, {
                      tracker: payload.tracker || '',
                      commandName: 'send',
                      arguments: [
                          'pageview',
                          args
                      ]
                  });
              }
docs: pageview handler
  @method pageview
  @param {Object} payload payload object
  @param {Object} payload.tracker page title
  @param {Object} payload.title page title
  @param {Object} payload.location page location
  @param {Object} payload.url current url
  @param {Function} calback callback function