Representing dates & times

Note: The Date object is now considered legacy and should be avoided in new code. We will update this page with modern alternatives soon.

Date object

JavaScript does not have a date data type. However, you can use the Date object and its methods to work with dates and times in your applications. The Date object has a large number of methods for setting, getting, and manipulating dates. It does not have any properties.

JavaScript handles dates similarly to Java. The two languages have many of the same date methods, and both languages store dates as the number of milliseconds since midnight at the beginning of January 1, 1970, UTC, with a Unix Timestamp being the number of seconds since the same instant. The instant at the midnight at the beginning of January 1, 1970, UTC is called the epoch.

The Date object range is -100,000,000 days to 100,000,000 days relative to the epoch.

To create a Date object:

js
const dateObjectName = new Date([parameters]);

where dateObjectName is the name of the Date object being created; it can be a new object or a property of an existing object.

Calling Date without the new keyword returns a string representing the current date and time.

The parameters in the preceding syntax can be any of the following:

  • Nothing: creates today's date and time. For example, today = new Date();.
  • A string representing a date, in many different forms. The exact forms supported differ among engines, but the following form is always supported: YYYY-MM-DDTHH:mm:ss.sssZ. For example, xmas95 = new Date("1995-12-25"). If you omit hours, minutes, or seconds, the value will be set to zero.
  • A set of integer values for year, month, and day. For example, xmas95 = new Date(1995, 11, 25).
  • A set of integer values for year, month, day, hour, minute, and seconds. For example, xmas95 = new Date(1995, 11, 25, 9, 30, 0);.

Methods of the Date object

The Date object methods for handling dates and times fall into these broad categories:

  • "set" methods, for setting date and time values in Date objects.
  • "get" methods, for getting date and time values from Date objects.
  • "to" methods, for returning string values from Date objects.
  • parse and UTC methods, for parsing Date strings.

With the "get" and "set" methods you can get and set seconds, minutes, hours, day of the month, day of the week, months, and years separately. There is a getDay method that returns the day of the week, but no corresponding setDay method, because the day of the week is set automatically. These methods use integers to represent these values as follows:

  • Seconds and minutes: 0 to 59
  • Hours: 0 to 23
  • Day: 0 (Sunday) to 6 (Saturday)
  • Date: 1 to 31 (day of the month)
  • Months: 0 (January) to 11 (December)
  • Year: years since 1900

For example, suppose you define the following date:

js
const xmas95 = new Date("1995-12-25");

Then xmas95.getMonth() returns 11, and xmas95.getFullYear() returns 1995.

The getTime and setTime methods are useful for comparing dates. The getTime method returns the number of milliseconds since the epoch for a Date object.

For example, the following code displays the number of days left in the current year:

js
const today = new Date();
const endYear = new Date(1995, 11, 31, 23, 59, 59, 999); // Set day and month
endYear.setFullYear(today.getFullYear()); // Set year to this year
const msPerDay = 24 * 60 * 60 * 1000; // Number of milliseconds per day
let daysLeft = (endYear.getTime() - today.getTime()) / msPerDay;
daysLeft = Math.round(daysLeft); // Returns days left in the year

This example creates a Date object named today that contains today's date. It then creates a Date object named endYear and sets the year to the current year. Then, using the number of milliseconds per day, it computes the number of days between today and endYear, using getTime and rounding to a whole number of days.

The parse method is useful for assigning values from date strings to existing Date objects. For example, the following code uses parse and setTime to assign a date value to the ipoDate object:

js
const ipoDate = new Date();
ipoDate.setTime(Date.parse("Aug 9, 1995"));

Example

In the following example, the function JSClock() returns the time in the format of a digital clock.

js
function JSClock() {
  const time = new Date();
  const hour = time.getHours();
  const minute = time.getMinutes();
  const second = time.getSeconds();
  let temp = String(hour % 12);
  if (temp === "0") {
    temp = "12";
  }
  temp += (minute < 10 ? ":0" : ":") + minute;
  temp += (second < 10 ? ":0" : ":") + second;
  temp += hour >= 12 ? " P.M." : " A.M.";
  return temp;
}

The JSClock function first creates a new Date object called time; since no arguments are given, time is created with the current date and time. Then calls to the getHours, getMinutes, and getSeconds methods assign the value of the current hour, minute, and second to hour, minute, and second.

The following statements build a string value based on the time. The first statement creates a variable temp. Its value is hour % 12, which is hour in the 12-hour system. Then, if the hour is 0, it gets re-assigned to 12, so that midnights and noons are displayed as 12:00 instead of 0:00.

The next statement appends a minute value to temp. If the value of minute is less than 10, the conditional expression adds a string with a preceding zero; otherwise it adds a string with a demarcating colon. Then a statement appends a seconds value to temp in the same way.

Finally, a conditional expression appends "P.M." to temp if hour is 12 or greater; otherwise, it appends "A.M." to temp.