code: function defaultFormat(d) {
    if ((0, _DateUtils.isDate)(d)) {
      var year = d.getFullYear();
      var month = '' + (d.getMonth() + 1);
      var day = '' + d.getDate();
      return year + '-' + month + '-' + day;
    }
    return '';
  }
docs: The default function used to format a Date to String, passed to the `format`
  prop.
  @param {Date} d
  @return {String}