Right now we validate some of our proptype definitions, but we don't surface the issue until that component class is consumed. We should instead validate these, in `__DEV__` only as warnings when the class in created. This means that a call to `React.PropTypes.onOf('foo')` results in an immediate warning logged.

This is a relatively contained bit of code so would be a good candidate for somebody looking to start contributing to React.

var propType = getPropType(propValue);
  if (propType === 'object') {
    if (propValue instanceof Date) {
      return 'date';
    } else if (propValue instanceof RegExp) {
      return 'regexp';
    }
  }
  return propType;
}
function getClassName(propValue) {
  if (!propValue.constructor || !propValue.constructor.name) {
    return ANONYMOUS;
  }
  return propValue.constructor.name;
}
module.exports = ReactPropTypes;