Web Development

JavaScript Dates

JavaScript Dates is section 7 of Beginner’s Guide to JavaScript.

Do you have any idea how the computer calculate the age of a person when input the birth date. For humans it is a easy task, because our brain can easily process it by calculating the year difference. But how the computer do it. For that we should input the date as a date object, where we separately say this is our year part, this is our month part and this is our day part and so on.. The Date object in JS lets you work with dates with years, months, days, minutes, seconds, milliseconds. Date objects are static, not dynamic. The computer time is ticking, but date objects, once created, are not.

[code language=”js”]


[/code]

Mon Oct 20 2014 10:24:36 GMT+0530 (Sri Lanka Standard Time)

Above shows the output of the code segment. When you display a date object in HTML, it is automatically converted to a string, with the toString() method. The toUTCString() method converts a date to a UTC string (a date display standard).

Mon, 20 Oct 2014 06:15:31 GMT

The toDateString() method converts a date to a more readable format.

Mon Oct 20 2014

Date objects are created with the new Date() constructor. There are 4 ways of initiating a date.

new Date()

new Date(milliseconds)

new Date(dateString)

new Date(year, month, day, hours, minutes, seconds, milliseconds)

Using new Date(), without parameters, creates a new date object with the current date and time. Using new Date(), with a date string, creates a new date object with the specified date and time. Using new Date(), with a number, creates a new date object with number of millisecond since 1970/01/01. JavaScript dates are calculated in milliseconds from 01 January, 1970 00:00:00 Universal Time (UTC). One day contains 86,400,000 millisecond. Using new Date(), with 7 numbers, creates a new date object with the specified date and time. The 7 numbers specify the year, month, day, hour, minute, second, and millisecond, in that order. Important thing is JavaScript counts months from 0 to 11. January is 0. December is 11.

Date Methods

Date methods let you get and set date values (years, months, days, minutes, seconds, milliseconds)

Date Get Methods

Get methods are used for getting a part of a date. Here are the most common (alphabetically).

Method Description
getDate() Get the day as a number (1-31)
getDay() Get the weekday a number (0-6)
getFullYear() Get the four digit year (yyyy)
getHours() Get the hour (0-23)
getMilliseconds() Get the milliseconds (0-999)
getMinutes() Get the minutes (0-59)
getMonth() Get the month (0-11)
getSeconds() Get the seconds (0-59)
getTime() Get the time (milliseconds since January 1, 1970)

Date Set Methods

Set methods are used for setting a part of a date. Here are the most common (alphabitically)

Method Description
setDate() Set the day as a number (1-31)
setFullYear() Set the year (optionally month and day yyyy.mm.dd)
setHours() Set the hour (0-23)
setMilliseconds() Set the milliseconds (0-999)
setMinutes() Set the minutes (0-59)
setMonth() Set the month (0-11)
setSeconds() Set the seconds (0-59)
setTime() Set the time (milliseconds since January 1, 1970)

Parsing Dates

If you have an input value (or any string), you can use the Date.parse() method to convert it to milliseconds. Date.parse() returns the number of milliseconds between the date and January 1, 1970.

var msec = Date.parse(“March 21, 2012”)

The parameter of the parse method is not a date. It is just a string which says about a date where you cannot use it for any calculations. And we are converting that string into a actual date object, so we can do any date related calculations like as the follows.

var d = new Date(msec);

Compare Dates

Dates can easily be compared with comparison operators.

someday > today


 

What’s Next?

Learn what includes in JavaScript Boolean

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About the author

Sandeep Likhar

Sandeep Likhar from Indore India, Blogger, eBook Designer and Founder of LetsDnD. Having five years of experience in industry as a Digital Publishing Expert and eBook Converter providing services to Authors, Publishers and distributors worldwide. Proficient in converting books into various formats HTML, epub, mobi, word, PDF including all major online platforms iTunes, Kobo, Kindle, Createspace, B&N, Smashwords and more.

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