Creating a date object from a date string is one day older

Question

I have a function where I convert a date string or a datetime string into a date object with time set to 00:00:00 - basically truncating the time.

/**
 * @param dateString - can either be 2023-07-13 or 2023-07-13 03:03:03
 */
const removeTime = (dateString: string): Date | undefined => {
    if (isValid(new Date(dateString))) {
        const timestamp = new Date(dateString);

        console.log('PARAM', dateString);
        console.log('NATIVE', timestamp);
        console.log('BEFORE TRUNCATE', format(timestamp, Constants.FORMAT_DATE));
        console.log(
            'AFTER TRUNCATE',
            format(
                new Date(timestamp.getFullYear(), timestamp.getMonth(), timestamp.getDate()),
                Constants.FORMAT_DATE
            )
        );

        return new Date(timestamp.getFullYear(), timestamp.getMonth(), timestamp.getDate());
    } else {
        return undefined;
    }
};

Please note that both the isValid and format calls are coming in from date-fns.

My problem is that the new Date(dateString) call sets the day back by 1.

PARAM:           2023-07-13
NATIVE:          Wed Jul 12 2023 18:00:00 GMT-0600 (Mountain Daylight Time)
BEFORE TRUNCATE: 2023-07-12
AFTER TRUNCATE:  2023-07-12

My Constants.FORMAT_DATE is yyyy-MM-dd.

ADDITIONAL INFO

It looks like this is only an issue if the dateString doesn't have a time part to it (i.e. 2023-07-13). The function actually works just fine if the string contains a time (i.e. 2023-07-13 03:03:03).

PARAM:           2023-07-13 11:26:11
NATIVE:          Thu Jul 13 2023 11:26:11 GMT-0600 (Mountain Daylight Time)
BEFORE TRUNCATE: 2023-07-13
AFTER TRUNCATE:  2023-07-13

Answer 1

You should add the timezone offset:

const isValid = dt => !isNaN(+dt);

const removeTime = (dateString) => {
    const dt = new Date(dateString);
    if (!isValid(dt )) {
      return;
    }
    dt.setMinutes(dt.getMinutes() + dt.getTimezoneOffset());
    return new Date(dt.getFullYear(), dt.getMonth(), dt.getDate());
};

console.log(removeTime('2023-07-13').toString());
console.log(removeTime('2023-07-13 03:03:03').toString());