Go time.Time type with custom format for UnmarshalJSON and MarshalJSON

jsondate.go

// JsonDate reflects the date format "yyyy-mm-dd" used in the API and the calendar component in the frontend.
type JsonDate time.Time

// UnmarshalJSON parses json dates
func (j *JsonDate) UnmarshalJSON(b []byte) error {
	s := strings.Trim(string(b), "\"")
	t, err := time.Parse("2006-01-02", s)
	if err != nil {
		return err
	}
	*j = JsonDate(t)
	return nil
}

// MarshalJSON outputs json dates
func (j *JsonDate) MarshalJSON() ([]byte, error) {
	return []byte("\"" + j.Format("2006-01-02") + "\""), nil
}

// Format json dates
func (j JsonDate) Format(s string) string {
	t := time.Time(j)
	return t.Format(s)
}

// String returns json dates in printable form
func (j JsonDate) String() string {
	return j.Format("2006-01-02")
}