Date and Time

Date and Time are displayed in a format that humans can understand. JavaScript understands dates based on timestamps. Timestamp specified as milliseconds elapsed since January 1st, 1970 (Unix time).

To start using the date object we need to create or instantiate a new date object.
We can do it in 4 different ways.

1st way is used to show the current date and time. The other 3 way allows us to work with specific date and times.

Method 1

let myDate = new Date();
console.log(myDate);//displays date, time and standard.

/*
    OUTPUT
    2023-08-31T04:28:13.608Z
*/

Method 2

let milliseconds = new Date(92347687467);//Number of milliseconds elapsed since January 1st 1970.
console.log(milliseconds.getFullYear());

/*
    OUTPUT
    1972
*/

Method 3

let currentDate = new Date(2023, 1, 12, 5, 3, 5, 5);// helps to display particular year, month, date, time, minute, seconds and milliseconds.
console.log(currentDate.toLocaleString());

/*
    OUTPUT
    12/2/2023, 5:03:05 am
*/

Method 4

let dateTimeString = new Date("Jan 22 2023");
console.log(dateTimeString)//Sun Jan 22 2023 00:00:00 GMT+0530 (India Standard Time)
let dateTimeString1 = new Date("Jan 22 2023 07:02:05");
console.log(dateTimeString1)//Sun Jan 22 2023 07:02:05 GMT+0530 (India Standard Time)
/*
    OUTPUT
    2023-01-21T18:30:00.000Z
    2023-01-22T01:32:05.000Z
*/

various methods that allow you to interact with the timestamp stored in the date

• Interact wth timestamp directly using getTime() and setTime() methods.
• All Static methods ( Date.now(), Date.parse()) return timestamps(timezone) instead of Date objects.
• The Date() constructor can be called with a timestamp as the only argument.

The Date() constructor can be called with two or more arguments, in which case they are interpreted as the year, month, day, hour, minute, second, and millisecond, respectively, in local time.

Date time string format

The JavaScript specification only specifies one format to be universally supported.

That is, YYYY-MM-DDTHH:mm:ss.sssZ

• YYYY is the year, with four digits (0000 to 9999).
• MM is the month, with two digits (01 to 12). The default is 01.
• DD is the day of the month, with two digits (01 to 31). The Default is 01.
• T is a literal character, which indicates the beginning of the time part of the string. The T is required when specifying the time part.
• HH is the hour, with two digits (00 to 23). As a special case, 24:00:00 is allowed, and is interpreted as midnight at the beginning of the next day. The Default is 00.
• mm is the minute, with two digits (00 to 59). The default is 00.
• ss is the second, with two digits (00 to 59). The default is 00.
• sss is the millisecond, with three digits (000 to 999). The default is 000.
• Z is the timezone offset, which can either be the literal character Z (indicating UTC), or + or - followed by HH:mm, the offset in hours and minutes from UTC.

Various components can be omitted, so the following are all valid.

• Date-only form: YYYY, YYYY-MM, YYYY-MM-DD
• Date-time form: one of the above date-only forms, followed by T, followed by HH:mm, HH:mm:ss, or HH:mm:ss.sss.

For example, "2011-10-10" (date-only form), "2011-10-10T14:48:00" (date-time form), or "2011-10-10T14:48:00.000+09:00" (date-time form with milliseconds and time zone) are all valid date time strings.

Other ways to format a date

• toISOString() returns a string in the format 1970-01-01T00:00:00.000Z
• toJSON() calls toISOString() and returns the result.
• toString() returns a string in the format Thu Jan 01 1970 00:00:00 GMT+0000(Coordinated Universal Time).
• toDateString() returns the date parts of the string.
• toTimeString() returns the time parts of the string.
• toLocaleDateString(), toLocaleTimeString(), and toLocaleString() use locale-specific date and time formats, usually provided by the Intl API.

console.log(myDate.toDateString());//displays date
console.log(myDate.toTimeString());//displays time and standard
console.log(myDate.toLocaleString());//displays date and time
console.log(myDate.toLocaleDateString());//displays date only
console.log(myDate.toLocaleTimeString());//displays time only

/*
    OUTPUT
    Thu Aug 31 2023
    11:27:19 GMT+0530 (India Standard Time)
    31/8/2023, 11:27:19 am
    31/8/2023
    11:27:19 am
*/

Static Methods

Date.now() - Return the number of milliseconds elapsed since January 1, 1970, 00:00:00 UTC.

Date.parse() - Return the time difference in milliseconds from, January 1, 1970, till the date we provide.

Date.UTC() - Return the number of milliseconds in a Date object since January 1, 1970, 00:00:00, universal time.

Instance Methods

There are two groups of Date methods. Both groups make use of both local and UTC timestamps.

• get
• set

Let's see some of the get methods using local time.

Date.getDate() - Returns the current date of the month from a given Date object. The return value is in between 1 to 31.

Date.getDay() - Returns the current day of the week from a given Date object. The return value is in between 0 to 6.

Date.getMonth() - Returns the current month of the year from a given Date object. The return value is in between 0 to 11.

Date.getFullYear() - Returns the current month of the year from a given Date object. The return value is in between 0 to 11.

Date.getHours() - Returns hours from a given Date object. The return value is in between 0 to 23.

Date.getMiutes() - Returns minutes from a given Date object. The return value is in between 0 to 59.

Date.getSeconds() - Returns seconds from a given Date object. The return value is in between 0 to 59.

Let's see some of the set methods using local time.

Date.setDate() - Used to set the date of the month to the date object. The value ranges between 1 to 31.

Date.setMonth() - Used to set the Month of the year to the date object. The value ranges between 0 to 11.

Date.setFullYear() - Used to set year into a date object. It can also be used to set setMonth() and setDate() as well.

Date.setHours() - Used to set the hour value into the date object. It can also be used to set setMinutes(), setSeconds() and setMilliseconds().

date.toLocaleString() - Used to SET date and time into strings using local time.

 let newDate = new Date();
console.log(
    newDate.toLocaleString('default', 
    {
        month: "long",
        weekday: "long",
        day: "numeric",
        year: "2-digit"
    })
);

/*
    OUTPUT

    Thursday, 31 August, 23
*/

Conclusion

We have covered creating date objects and using the inbuilt methods. This will give you a kickstart to learn the date and time.

Resources

MDN

Chai aur Code

Dev Dreamer

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