JAVASCRIPT: A Beginner’s Guide to Learning the Basics of JavaScript Programming (2015)

Chapter 20. Dates and Time

The Date Object

The data object enables basic storage and recall of dates and times. Below is the syntax for the date object:

Below are the parameters of the date object:

Parameter	Description
dateObi	Mandatory. This is used to assign the Date object.
dateVal	Mandatory. When a numeric value, this parameter signifies the number of milliseconds in UCT between the certain time and Jan 1 1970 midnight. If dateVal is a string, this will be parsed based on the rules in JavaScript. Meanwhile, the dateVal argument could also be a VT_DATE value as generated from certain objects ActiveX.
ms	Optional. Refers to the number between zero to 999, which specifies milliseconds.
seconds	Optional. Should be included if you add milliseconds. This refers to the number from zero to 59, which signifies the seconds.
minutes	Optional. Should be included if you add seconds. This refers to the number from zero to 59, which signifies the minutes.
hours	Optional. Should be included if you add minutes. This refers to the number from zero to 23 (mn to 11:00 pm, which refers to the hour)
month	Mandatory. The month is a number from zero to 11 (Jan to Dec)
year	Mandatory. Should be complete year such as 1996 and not 96
date	Mandatory. The date as an integer in between one and 31.

Take note that a data object will contain a number signifying a certain occurrence in time to within a millisecond. When the value of an argument is larger than the range or this is a negative number. Other stored values will be modified. For instance, if you enter 240 seconds, the JavaScript will redefine the number as four minutes.

When the number is NaN, the object will not represent a particular time instant. When you pass no parameters to the Date object, it will be initialized to UTC. Remember, a value should be provided to the object before using this. The date range could be signified in the object Date about 285616 years before and after Jan 1 1970.

The example below shows the use of the Date object.

Date Object Properties

There are two properties of the Date Object: prototype Property and constructor Property.

Property	Description
Prototype	Yield a reference to the objects class prototype
Constructor	Specifies the function that creates an object

Date Object Functions

Functions	Description
Date.UTC	Yields the number of milliseconds between Jan 1, 1970 UTC and the date added
Date.parse	Parses that string that contains a date, and yields the milliseconds between the date and midnight Jan 1, 1970 UTC
Date.now	Yields the milliseconds between Jan 1, 1970 and the present time and date

Date Object Methods

Below is the list of Date object methods:

Method	Description
getFullYear	Yields the year value in local time.
getHours	Yields the hours value in local time.
getDay	Yields the week day in local time.
getDate	Yields the month day through local time
getMinutes	Yields the minute value in local time
getMonth	Yields the month value in local time
getSeconds	Yields the seconds value in local time
getMilliseconds	Yields the milli seconds in local time
getTime	Yields the time within an object Date as the no. of milli seconds since Jan 1, 1970 midnight
getUTCDate	Yields the month day in UTC
getUTCDay	Yields the week day in UTC
getUTCFullYear	Yields the year in UTC
getUTCHours	Yields the hours in UTC
getUTCMilliseconds	Yields the milliseconds in UTC
getUTCMinutes	Yields the minutes in UTC
getUTCMonth	Yields the month in UTC
getSeconds	Yields the seconds in UTC
getTimezoneOffset	Yields the minute difference between the UTC and the computer
getYear	Yields the value year
getVarDate	Yields the value VT_DATE in a Date object
isPrototype	Yields a Boolean value, which signifies if an object is existing in the prototype chain of an object
hasOwnProperty	Yields the Boolean value, which signifies if an object has a property with the particular name
propertyIsEnumerable	Yields a Boolean value, which signifies if a certain property is a composition of an object and if it is enumerable.
setSeconds	Defines the seconds value in local time
setMonth	Defines the month value in local time
setMinutes	Defines the minute value in local time
setMilliseconds	Defines the milliseconds value in local time
setHours	Defines the hour value in local time
setDate	Defines the numerical month day in local time
setFullYear	Defines the value year in local time
setUTCSeconds	Defines the seconds value in UTC
setUTCMonth	Defines the month value in UTC
setUTCMinutes	Defines the minutes value in UTC
setUTCMilliseconds	Defines the milliseconds value in UTC
setUTCHours	Defines the hours value in UTC
setUTCFullYear	Defines the year in UTC
setUTCDate	Defines the numerical month day in UTC
setTime	Defines the date and time value in object Date
setYear	Defines the year value in loc time
toLocaleTime	Yields a time as a value string suitable to the current local of the host environment
toLocaleDateString	Yields a data in string value suitable to the current local of the host environment
toDateString	Yields a data in value string
toISOString	Yields a date in value string but in ISO format
toGMTString	Yields a date changes to a string in GMT
toJSON	Yields a changed data of type object prior to the JSON serial
valueOf	Yields the prime value of a defined object
toTimeString	Yields the time as a string value
toString	Yields a string representation of the object
toUTCString	Yields a date changed to a string in UTC

Calculating Dates and Time using JavaScript

It is possible to use the object Date in order to perform usual clock and calendar tasks like computing elapsed time and date comparison.

Setting up Date to the Existing Date

If you make an instance of the object Date without defining a date, it will return a value, which will signify the present date and time, which also includes the millisecond, the second, the minute, hour, day, and year. You can then modify or read this date and time.

The example below shows the process of instantiating a date without the use of any type of parameters and showing the result in mm-dd-yy format.

Setting up a Particular Date

It is possible to set a particular date through passing string date to the constructor.

The time zone shown in the date string is suitable to the time zone defined in the local machine. It is a good thing that JS is dynamic about the string format used as the parameter. For instance, you can use “1-16-2016”, “January 16, 2016”, or “16 Jan 2016”.