How to use the fullcalendar.EventSource.prototype function in fullcalendar

applyManualStandardProps(rawProps) {
    let superSuccess = EventSource.prototype.applyManualStandardProps.apply(this, arguments)
    let googleCalendarId = rawProps.googleCalendarId

    if (googleCalendarId == null && rawProps.url) {
      googleCalendarId = parseGoogleCalendarId(rawProps.url)
    }

    if (googleCalendarId != null) {
      this.googleCalendarId = googleCalendarId

      return superSuccess
    }

    return false
  }