Getting the start of a day for a specific date in JavaScript while considering the timezone

Question

Getting the start of a day for a specific date in JavaScript while considering the timezone

I'm having trouble determining the start of a day while factoring in timezones using javascript. Consider this example:

   var raw_time = new Date(this.created_at);
   var offset_time = new Date(raw_hour.getTime() + time_zone_offset_in_ms);

   // This resets timezone to server timezone
   var offset_day = new Date(offset_time.setHours(0,0,0,0))
   // always returns 2011-12-08 05:00:00 UTC, no matter what the offset was!

   // This has the same issue:
   var another_approach_offset_day = new Date(offset_time.getFullYear(),offset_time.getMonth(),offset_time.getHours())

When I provide a Pacific Timezone offset, I expect to receive: 2011-12-08 08:00:00 UTC and so forth.

What is the correct way to achieve this?

I believe part of the problem lies in the fact that the setHours method sets the hour (from 0 to 23) based on local time.

Please note that I am utilizing javascript embedded in mongo, restricting me from employing any additional libraries.

Thank you!

Wow, this was quite a challenge for me, but I managed to come up with a final solution. The key was realizing I needed to use setHours or SetUTCHours to find the start of a day - my only options being system time and UTC. So, I obtain the beginning of a UTC day and then adjust for the offset!

// Objective: determine the start of a day given a time and timezone
function(timestamp, selected_timezone_offset) {
  var raw_time = new Date(timestamp)
  var offset_time = new Date(raw_time.getTime() + selected_timezone_offset);
  offset_time.setUTCHours(0,0,0,0);
  var beginning_of_day = new Date(offset_time.getTime() - selected_timezone_offset);
  return beginning_of_day;
}

javascript mongodb timezone

Answer 1

Answer №1

When working with dates in JavaScript, it's important to remember that all dates are stored as UTC. This means that the serial number returned by date.valueOf() represents the number of milliseconds since 1970-01-01 00:00:00 UTC. However, when you view a date using methods like .toString() or .getHours(), you actually see the value in local time - the time of the system running the script. To retrieve the value in UTC, you can use methods such as .toUTCString() or .getUTCHours().

While you can't directly obtain a date in any arbitrary timezone (it's either UTC or local), you can still display a string representation of a date in your desired timezone by adjusting for the UTC offset. The simplest way to do this is by subtracting the UTC offset from the date and then calling .getUTCHours() or .toUTCString():

var d = new Date();
d.setMinutes(d.getMinutes() - 480); // adjust for pacific standard time
d.toUTCString(); // returns "Fri, 9 Dec 2011 12:56:53 UTC"

If you want to replace the "UTC" at the end with something like "PST", you can simply perform a string substitution:

d.toUTCString().replace(/UTC$/, "PST");

Edit: When dealing with timezones crossing date boundaries, you need not worry. If you provide setHours() with a negative value, it will correctly handle the subtraction of hours from midnight on the previous day. For example:

var d = new Date(2011, 11, 10, 15); // Represents Dec 10, 2011 at 3pm local time
d.setHours(-1);                     // Represents Dec 9, 2011 at 11pm local time
d.setHours(-24);                    // Represents Dec 8, 2011 at 12am local time
d.setHours(52);                     // Represents Dec 10, 2011 at 4am local time

Answer 2

When working with dates in JavaScript, it's important to remember that all dates are stored as UTC. This means that the serial number returned by date.valueOf() represents the number of milliseconds since 1970-01-01 00:00:00 UTC. However, when you view a date using methods like .toString() or .getHours(), you actually see the value in local time - the time of the system running the script. To retrieve the value in UTC, you can use methods such as .toUTCString() or .getUTCHours().

While you can't directly obtain a date in any arbitrary timezone (it's either UTC or local), you can still display a string representation of a date in your desired timezone by adjusting for the UTC offset. The simplest way to do this is by subtracting the UTC offset from the date and then calling .getUTCHours() or .toUTCString():

var d = new Date();
d.setMinutes(d.getMinutes() - 480); // adjust for pacific standard time
d.toUTCString(); // returns "Fri, 9 Dec 2011 12:56:53 UTC"

If you want to replace the "UTC" at the end with something like "PST", you can simply perform a string substitution:

d.toUTCString().replace(/UTC$/, "PST");

Edit: When dealing with timezones crossing date boundaries, you need not worry. If you provide setHours() with a negative value, it will correctly handle the subtraction of hours from midnight on the previous day. For example:

var d = new Date(2011, 11, 10, 15); // Represents Dec 10, 2011 at 3pm local time
d.setHours(-1);                     // Represents Dec 9, 2011 at 11pm local time
d.setHours(-24);                    // Represents Dec 8, 2011 at 12am local time
d.setHours(52);                     // Represents Dec 10, 2011 at 4am local time

Answer 3

Answer №2

Have you considered the source of the time_zone_offset_in_ms variable you are using? It might be unreliable; instead, you could utilize Date's getTimezoneOffset() method for accuracy. You can find an example at this URL:

http://www.example.com/jsref/getTimezoneOffset

Answer 4

Have you considered the source of the time_zone_offset_in_ms variable you are using? It might be unreliable; instead, you could utilize Date's getTimezoneOffset() method for accuracy. You can find an example at this URL:

http://www.example.com/jsref/getTimezoneOffset

Answer 5

Answer №3

To retrieve the date from a varying date string, use the code snippet below:

let selectedDate = new Date(this.$picker.data('date'));
let todayDate = new Date();
todayDate.setHours(0, -selectedDate.getTimezoneOffset(), 0, 0);

(inspired by a previous project's implementation)

Answer 6

To retrieve the date from a varying date string, use the code snippet below:

let selectedDate = new Date(this.$picker.data('date'));
let todayDate = new Date();
todayDate.setHours(0, -selectedDate.getTimezoneOffset(), 0, 0);

(inspired by a previous project's implementation)

Answer 7

Answer №4

let currentDate = new Date();
let startOfDay = new Date(currentDate.getTime() - currentDate.getTime() % 86400000);

This code snippet will generate the start of the current day.

Answer 8

let currentDate = new Date();
let startOfDay = new Date(currentDate.getTime() - currentDate.getTime() % 86400000);

This code snippet will generate the start of the current day.

Answer 9

Answer №5

If you want to work with date and time in different timezones, one useful tool is the Intl.DateTimeFormat feature. Another option is to look at how luxon library deals with timezones.

The following code snippet demonstrates how you can convert any date with any timezone to its beginning or end of the day:

const beginingOfDay = (options = {}) => {
  const { date = new Date(), timeZone } = options;
  const parts = Intl.DateTimeFormat("en-US", {
    timeZone,
    hourCycle: "h23",
    hour: "numeric",
    minute: "numeric",
    second: "numeric",
  }).formatToParts(date);
  const hour = parseInt(parts.find((i) => i.type === "hour").value);
  const minute = parseInt(parts.find((i) => i.type === "minute").value);
  const second = parseInt(parts.find((i) => i.type === "second").value);
  return new Date(
    1000 *
      Math.floor(
        (date - hour * 3600000 - minute * 60000 - second * 1000) / 1000
      )
  );
};

const endOfDay = (...args) =>
  new Date(beginingOfDay(...args).getTime() + 86399999);

const beginingOfYear = () => {};

console.log(beginingOfDay({ timeZone: "GMT" }));
console.log(endOfDay({ timeZone: "GMT" }));
console.log(beginingOfDay({ timeZone: "Asia/Tokyo" }));
console.log(endOfDay({ timeZone: "Asia/Tokyo" }));

Answer 10

If you want to work with date and time in different timezones, one useful tool is the Intl.DateTimeFormat feature. Another option is to look at how luxon library deals with timezones.

The following code snippet demonstrates how you can convert any date with any timezone to its beginning or end of the day:

const beginingOfDay = (options = {}) => {
  const { date = new Date(), timeZone } = options;
  const parts = Intl.DateTimeFormat("en-US", {
    timeZone,
    hourCycle: "h23",
    hour: "numeric",
    minute: "numeric",
    second: "numeric",
  }).formatToParts(date);
  const hour = parseInt(parts.find((i) => i.type === "hour").value);
  const minute = parseInt(parts.find((i) => i.type === "minute").value);
  const second = parseInt(parts.find((i) => i.type === "second").value);
  return new Date(
    1000 *
      Math.floor(
        (date - hour * 3600000 - minute * 60000 - second * 1000) / 1000
      )
  );
};

const endOfDay = (...args) =>
  new Date(beginingOfDay(...args).getTime() + 86399999);

const beginingOfYear = () => {};

console.log(beginingOfDay({ timeZone: "GMT" }));
console.log(endOfDay({ timeZone: "GMT" }));
console.log(beginingOfDay({ timeZone: "Asia/Tokyo" }));
console.log(endOfDay({ timeZone: "Asia/Tokyo" }));

Getting the start of a day for a specific date in JavaScript while considering the timezone

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

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