index.js
function update(instance) {
  instance.isValid = isValid(instance._date);
  instance.timeString = instance.toString();
  return instance;
}
function update(instance) {
  instance.isValid = isValid(instance._date);
  instance.timeString = instance.toString();
  return instance;
}
function update ( instance ) { instance . isValid = isValid ( instance . _date ) ; instance . timeString = instance . toString ( ) ; return instance ; }
Update 'instance' state
@param {Time} instance
@returns {Time}
Update instance state