The Date Object

Date objects store dates and provide many methods to extract the hours, minutes, and so on parts of dates. There are a number of different ways to create Date objects, such as the following:

 var date1 = new Date()  var date1 = new Date(dateVal)  var date1 = new Date(year, month, date[, hours[, minutes[, seconds[, ms]]]])

Note the use of the keyword new here. Both the Date and String types are object types, and you use the new keyword to create objects, as discussed in Chapter 2, "The JavaScript Language: Data, Operators, and Branching." As you see here, you can pass values to the Date type's constructor (constructors were discussed in Chapter 2; they're methods that create objects and have the same name as the object you're creating, such as Date ) to indicate how to configure the new object. Here are what the parameters mean in this case:

dateVal . If a number, dateVal is the number of milliseconds in Universal Coordinated Time (UTC) between the date you want to use and midnight January 1, 1970. If a string, dateVal is parsed using the Date object's parse method.
year . The four-digit year.
month . The month (as an integer between 0 and 11, where January = 0).
date . The day of the month (as an integer between 1 and 31).
hours . The hour as an integer from (0 to 23, which corresponds to midnight to 11 p.m.).
minutes . The minutes as an integer (from 0 to 59).
seconds . The seconds as an integer (from 0 to 59).
ms . An integer from 0 to 999 that gives the milliseconds (one-thousandths of a second).

If you don't pass any parameters to the Date constructor, the created Date object will correspond to the current date. When you create a new date, you can use the various Date object methods to get the parts of the date, such as the number of hours:

 var date1 = new Date()  var hours1 = date1.getHours()

You can see the methods of the Date object in Table 18.1.

Table 18.1. The Methods of the Date Object

Method	NS2	NS3	NS4	NS6	IE3a	IE3b	IE4	IE5	IE5.5	IE6
`getDate`	x	x	x	x	x	x	x	x	x	x
	Returns: Integer
	Returns the day of the month, 1-31.
	Syntax: `date` `.getDate()` .
`getDay`	x	x	x	x	x	x	x	x	x	x
	Returns: Integer
	Returns the day of the week, 0-6 (where Sunday = 0, and Saturday = 6).
	Syntax: `date` `.getDay()` .
`getFullYear`			x	x		x	x	x	x	x
	Returns: Integer
	Gets the full, four-digit year.
	Syntax: `date` `.getFullYear()` .
`getHours`	x	x	x	x	x	x	x	x	x	x
	Returns: Integer
	Gets the hour of the day since midnight, 0-]23.
	Syntax: `date` `.getHours()` .
`getMilliseconds`			x	x		x	x	x	x	x
	Returns: Integer
	Returns the milliseconds value in a `Date` object using local time.
	Syntax: `date` `.getMilliseconds()` .
`getMinutes`	x	x	x	x	x	x	x	x	x	x
	Returns: Integer
	Returns the minutes value in a `Date` object using local time.
	Syntax: `date` `.getMinutes()` .
`getMonth`	x	x	x	x	x	x	x	x	x	x
	Returns: Integer
	Returns the month value, 0-11 (January = 0) in the `Date` object using local time.
	Syntax: `date` `.getMonth()` .
`getSeconds`	x	x	x	x	x	x	x	x	x	x
	Returns: Integer
	Returns the seconds value in a `Date` object using local time. Returns 0-59.
	Syntax: `date` `.getSeconds()` .
`getTime`	x	x	x	x	x	x	x	x	x	x
	Returns: Integer
	Returns an integer value representing the number of milliseconds between midnight, January 1, 1970 and the time value in the `Date` object. In the Internet Explorer, the range of dates is approximately 285,616 years from either side of midnight, January 1, 1970. Negative numbers mean dates before 1970.
	Syntax: `date` `.getTime()` .
`getTimezoneOffset`
	x	x	x	x	x	x	x	x	x	x
	Returns: Integer
	Returns the difference in minutes between the time on the computer and UTC.
	Syntax: `date` `.getTimezoneOffset()` .
`getUTCDate`			x	x		x	x	x	x	x
	Returns: Integer
	Returns the day of the month in a `Date` object using UTC. Returns 1-31.
	Syntax: `date` `.getUTCDate()` .
`getUTCDay`			x	x		x	x	x	x	x
	Returns: Integer
	Returns the day of the week value in a `Date` object using UTC. Returns 0-6 (where 0 = Sunday).
	Syntax: `date` `.getUTCDay()` .
`getUTCFullYear`			x	x		x	x	x	x	x
	Returns: Integer
	Returns the four-digit year value in a `Date` object using UTC.
	Syntax: `date` `.getUTCFullYear()` .
`getUTCHours`			x	x		x	x	x	x	x
	Returns: Integer
	Returns the hours value in a `Date` object using UTC. returns 0-23.
	Syntax: `date` `.getUTCHours()` .
`getUTCMilliseconds`			x	x		x	x	x	x	x
	Returns: Integer
	Returns the milliseconds value in a `Date` object using UTC. Returns 0-999.
	Syntax: `date` `.getUTCMilliseconds()` .
`getUTCMinutes`			x	x		x	x	x	x	x
	Returns: Integer
	Returns the minutes value in a `Date` object using UTC. Returns 0-59.
	Syntax: `date` `.getUTCMinutes()` .
`getUTCMonth`			x	x		x	x	x	x	x
	Returns: Integer
	Returns the month value in a `Date` object using UTC. Returns 0-11 (January = 0).
	Syntax: `date` `.getUTCMonth()` .
`getUTCSeconds`			x	x		x	x	x	x	x
	Returns: Integer
	Returns the month value in a `Date` object using UTC. Returns 0-59.
	Syntax: `date` `.getUTCSeconds()` .
`getVarDate`							x	x	x	x
	Returns: `Date` object
	Returns the date using `VT_DATE` format, which you use when interacting with COM objects, ActiveX objects, or other objects that accept and return date values in `VT_DATE` format in the Internet Explorer.
	Syntax: `date` `.getVarDate()` .
`getYear`	x	x	x	x	x	x	x	x	x	x
	Returns: Integer
	This method is considered obsolete; use the `getFullYear` method instead. In the Internet Explorer, for the years 1900 though 1999, the year is a 2-digit integer value returned as the difference between the stored year and 1900. For dates outside that period, the 4-digit year is returned. In the Netscape Navigator, the year is returned as the difference between the stored year and 1900.
	Syntax: `date` `.getYear()` .
`parse`	x	x	x	x	x	x	x	x	x	x
	Returns: Integer
	Parses a string containing a date, and returns the number of milliseconds between that date and midnight, January 1, 1970. The acceptable date formats vary by browser, such as `"December 15, 2003 11:20 AM"` .
	Syntax: `Date.parse("dateString")` . Note that you don't need a `Date` object here, just the name `Date` .
`setDate`	x	x	x	x	x	x	x	x	x	x
	Returns: Nothing
	Sets the day of the month.
	Syntax: `date` `.setDate(` `value` `)` , where `value` is 1-31.
`setDay`	x	x	x	x	x	x	x	x	x	x
	Returns: Nothing
	Sets the day of the week.
	Syntax: `date` `.setDay(` `value` `)` , where `value` is 0-6 (Sunday = 0).
`setFullYear`			x	x		x	x	x	x	x
	Returns: Integer
	Sets the four-digit year.
	Syntax: `date` `.setFullYear(` `year` `)` , where `year` is the four-digit year.
`setHours`	x	x	x	x	x	x	x	x	x	x
	Returns: Nothing
	Sets the hour of the day in 24-hour time.
	Syntax: `date` `.setHours(` `value` `)` , where `value` is 0-23.
`setMilliseconds`			x	x		x	x	x	x	x
	Returns: Nothing
	Sets the number of milliseconds.
	Syntax: `date` `.setMilliseconds(` `value` `)` where `value` is 0-999.
`setMinutes`	x	x	x	x	x	x	x	x	x	x
	Returns: Nothing
	Sets the number of minutes.
	Syntax: `date` `.setMinutes(` `value` `)` , where `value` is 0-59.
`setMonth`	x	x	x	x	x	x	x	x	x	x
	Returns: Nothing
	Sets the month in the date.
	Syntax: `date` `.setMonth(` `value` `)` , where `value` is 0-11 (January = 0).
`setSeconds`	x	x	x	x	x	x	x	x	x	x
	Returns: Nothing
	Sets the seconds in the date.
	Syntax: `date` `.setSeconds(` `value` `)` , where `value` is 0-59.
`setTime`	x	x	x	x	x	x	x	x	x	x
	Returns: Nothing
	Sets the date and time using a millisecond value.
	Syntax: `date` `.setTime(` `value` `)` , where `value` is an integer value representing the number of elapsed seconds since midnight, January 1, 1970 Greenwich Mean Time (GMT).
`setUTCDate`			x	x		x	x	x	x	x
	Returns: Nothing
	Sets the day of the month in the `Date` object using UTC.
	Syntax: `date` `.setUTCDate(` `value` `)` , where `value` is 1-31.
`setUTCDay`			x	x		x	x	x	x	x
	Returns: Nothing
	Sets the day of the week in the `Date` object using UTC.
	Syntax: `date` `.setUTCDay(` `value` `)` , where `value` is 0-6 (Sunday = 0).
`setUTCFullYear`			x	x		x	x	x	x	x
	Returns: Nothing
	Sets the full year in the `Date` object using UTC.
	Syntax: `date` `.setUTCFullYear(` `value` `)` , where `value` is the four-digit year.
`setUTCHours`			x	x		x	x	x	x	x
	Returns: Nothing
	Sets the hour in the `Date` object using UTC.
	Syntax: `date` `.setUTCHours(` `value` `)` , where `value` is 0-23 in 24-hour time.
`setUTC Milliseconds`			x	x		x	x	x	x	x
	Returns: Nothing
	Sets the milliseconds value in the `Date` object using UTC.
	Syntax: `date` `.setUTCMilliseconds(` `value` `)` , where `value` is 0-999.
`setUTCMinutes`			x	x		x	x	x	x	x
	Returns: Nothing
	Sets the minutes value in the `Date` object using UTC.
	Syntax: `date` `.setUTCMinutes(` `value` `)` , where `value` is 0-59.
`setUTCMonth`			x	x		x	x	x	x	x
	Returns: Nothing
	Sets the minutes value in the `Date` object using UTC.
	Syntax: `date` `.setUTCMonth(` `value` `)` , where `value` is 0-11 (January = 0).
`setUTCSeconds`			x	x		x	x	x	x	x
	Returns: Nothing
	Sets the seconds value in the `Date` object using UTC.
	Syntax: `date` `.setUTCSeconds(` `value` `)` , where `value` is 0-59.
`setYear`	x	x	x	x	x	x	x	x	x	x
	Returns: Nothing
	This method is considered obsolete; use `setFullYear` instead. Sets the year value in the `Date` object.
	Syntax: `date` `.setYear(` `value` `)` , where `value` is the year.
`toDateString`									x	x
	Returns: String
	Returns a (browser-dependent) string holding the date.
	Syntax: `date` `.toDateString()` .
`toGMTString`	x	x	x	x	x	x	x	x	x	x
	Returns: String
	Returns a (browser-dependent) string holding the GMT date.
	Syntax: `date` `.toGMTString()` .
`toLocaleString`				x					x	x
	Returns: String
	Returns a (browser-dependent) string holding the local date in local format.
	Syntax: `date` `.toLocaleString()` .
`toLocaleDateString`				x					x	x
	Returns: String
	Returns a (browser-dependent) string holding the local date in UTC format.
	Syntax: `date` `.toLocaleDateString()` .
`toLocaleTimeString`				x					x	x
	Returns: String
	Returns a (browser-dependent) string holding the local time in local format.
	Syntax: `date` `.toLocaleTimeString()` .
`toString`	x	x	x	x	x	x	x	x	x	x
	Returns: String
	Returns a (browser-dependent) string holding the local time.
	Syntax: `date` `.toString()` .
`toTimeString`				x					x	x
	Returns: String
	Returns a (browser-dependent) string holding the time.
	Syntax: `date` `.toTimeString()` .
`toUTCString`			x	x		x	x	x	x	x
	Returns: String
	Returns the date converted to a string using UTC.
	Syntax: `date` `.toUTCString()` .
`UTC`	x	x	x	x	x	x	x	x	x	x
	Returns: Integer
	Returns the number of milliseconds between midnight, January 1, 1970 UTC (or GMT) and the given date.
	Syntax: `Date.UTC(` `year` `,` `month` `,` `day` `[,` `hours` `[,` `minutes` `[,` `seconds` `[,` `ms` `]]]])` . Note that you don't need a `Date` object here, just the `Date` name.
`valueOf`		x	x	x			x	x	x	x
	Returns: String
	Returns the date converted to a string using UTC.
	Syntax: `date` `.valueOf()` .

Tip

Note that days of the month are stored in 1-31 values in Date objects, but that days of the week are stored as 0-6 values, not 1-7.