code: function createdDate(key, value, prop) {
    var val = prop ? get(value, prop) : value;
    var str = val || key;
  
    var re = /^(\d{4})-(\d{2})-(\d{2})/;
    var m = re.exec(str);
    if (!m) return null;
    return String(m[1]) + String(m[2]) + String(m[3]);
  }
docs: Get the date from a specified property or key.
  
  @param  {String} `key` Key used as the fallback when the property is not on the value.
  @param  {Object} `value` Object to use when finding the property.
  @param  {String} `prop` Property string to use to get the date.
  @return {String} Date string in the format `YYYYMMDD` (e.g. 20150618)