_triggerSelectDate(day, month, year) {
    if (!this.props.disabled && !this.props.readOnly) {
      const selectedDate = day ? new Date(year, month, day) : undefined;

      if (has(this.props, 'valueLink')) {
        this.props.valueLink.requestChange(selectedDate);
      } else if (!has(this.props, 'value')) {
        this.setState({
          selectedDate,
          month,
          year,
        });
      }

      if (this.props.onUpdate) {
        this.props.onUpdate({
          value: selectedDate,
        });
      }
    }
  }
Depending on whether component is controlled or uncontrolled the function will update this.state.selectedDate.
It will also call props.onUpdate.