Angular 2 form validations start date <= end date

Question

I\'m trying to add validations such that the end date can\'t be before the start date. Unfortunately I have no idea how to do that, and I didn\'t find any helpful advice in

Answer 1

I am using moment, and in angular 7 to compare and validate dates, i use this function:

datesValidator(date1: any, date2: any): {[key:string]:any} | null {
    return (group: FormGroup): { [key: string]: any } | null => {
        let start = group.controls[date1].value;
        let end = group.controls[date2].value;
        let datum1 = _moment(start).startOf('day');
        let datum2 = _moment(end).startOf('day');
        if (_moment(datum1).isSameOrAfter(datum2)) {
           this.alert.red("Error: wrong period!"); //popup message
           return { 'error': 'Wrong period!' };        
        }
        return null; //period is ok, return null
    };
}