'fieldData.FROM_TIME': function(keyToGetData){
    return validator(function(value, options, model) {
        let fromTime = value;
        let toTime = model.get(keyToGetData);
        if(fromTime){
            let fromHours = fromTime.hours;
            let fromMins = fromTime.minutes;

            // make validation only if toTime is there
            if(toTime){
                let toHours = toTime.hours;
                let toMins = toTime.minutes;
                if(fromHours > toHours || ( fromHours===toHours && fromMins > toMins) ){
                    return 'From time must be earlier than To time.';
                }
            }
            return true;
        }
        return 'This field can not be blank';
    });
},

'fieldData.TO_TIME': function(keyToGetData){
    return validator(function(value, options, model) {
        let fromTime = model.get(keyToGetData);
        let toTime = value;

        if(toTime){
            let toHours = toTime.hours;
            let toMins = toTime.minutes;

            // make validation only if fromTime is there
            if(fromTime){
                let fromHours = fromTime.hours;
                let fromMins = fromTime.minutes;

                if(fromHours > toHours || (fromHours===toHours && fromMins >= toMins) ){
                    return 'To time must be later than From time.';
                }
            }
            return true;
        }
        return 'This field can not be blank';
    });
}