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javascriptdate-fns

How to calculate the first timestamp/Date of a specific day and the last second's timestamp?

I have a given date as Date-object in JavaScript.

From that particular date (e.g. 2024-16-01, 22:35), I want to go to the beginning of the day (2024-16-01, 00:00) and the end of the day (2024-16-01, 23:59).

I tried the library date-fns, but this gives wrong values.

import { addDays, addHours, endOfDay, startOfDay, subHours } from 'date-fns';

// d = new Date(...)
const startDate = subHours(startOfDay(d), hoursBefore);
const endDate = addHours(endOfDay(d), hoursAfter);

console.log('Date: ', d);
console.log('Start Of Day: ', startOfDay(d));
console.log('End Of Day: ', endOfDay(d));
console.log('startDate: ', startDate);
console.log('endDate: ', endDate);

Output:

Date:  2024-01-16T17:00:00.000Z
Start Of Day:  2024-01-16T17:00:00.000Z
End Of Day:  2024-01-17T16:59:59.999Z
startDate:  2024-01-16T05:00:00.000Z
endDate:  2024-01-17T21:59:59.999Z

As one can see, the values are totally different from what they actually should be. Is the timezone playing a disturbing role here? If so, how can I mitigate such risks of getting wrong values?

Or is there another approach how to deal with that?

Solution

  • startOfDay already returns:

    The start of a day

    So there is no need to combine it with subHours or addHours, just do startOfDay(d):

    const d = new Date();

const startDate = dateFns.startOfDay(d);
const endDate = dateFns.endOfDay(d);

console.log('Date: ', d);
console.log('Start Of Day: ', startDate);
console.log('End Of Day: ', endDate);
    <script src="https://cdnjs.cloudflare.com/ajax/libs/date-fns/1.28.5/date_fns.min.js"></script>

    Regarding the time-zone, you'll need date-fns-tz to convert it relative to your current zone / utc, please refer to: