Comments on: Mastering the date object in javascript

By: Dan

Dan — Wed, 18 Mar 2009 19:43:15 +0000

@bartek Thanks! I updated the code.

By: bartek

bartek — Wed, 18 Mar 2009 19:21:47 +0000

Thanks for great tips!
Remember that “getMonth()” returns the month as number between 0 and 11.
In your formatting example you need to increase month by one.

By: How to know if it’s a leap year | Javascript Kata

How to know if it’s a leap year | Javascript Kata — Thu, 19 Feb 2009 13:01:44 +0000

[...] the magic part of it. As I said in Mastering the date object in Javascript, there’s a special twist that let you work with dates differently than in most of the [...]

By: geoffrey.mcgill

geoffrey.mcgill — Tue, 18 Mar 2008 19:27:30 +0000

Hi Dan,

We’ve been working on a JavaScript Date library for a while that you might find useful.

http://www.datejs.com/

One major piece of functionality we include is a new Parser.

Parsing Example
alert(Date.parse(“next friday”));

Here’s a couple other samples which may be relevant to your samples.

Formatting Example
alert(new Date(“yyyy-MM-dd”));

Add/Subtract Example
new Date().add(5).days();
Date.today().add(-5).months();

Hope this helps.

By: Brian Reischl

Brian Reischl — Mon, 21 May 2007 14:44:16 +0000

I’ve been using Matt Kruse’s date formatting library and I find it works quite well. It definitely beats using string concatenation.

http://www.mattkruse.com/javascript/date/source.html

By: Andrew Vit

Andrew Vit — Sun, 20 May 2007 18:45:24 +0000

Dates are unusable when dealing with anything before 1970, so if you deal with birthdate input and need to calculate an age on the client side, don’t use Date to help with the arithmetic. I found it’s best to calculate age from separate year/month/day integers.

By: Dan

Dan — Fri, 18 May 2007 18:11:44 +0000

@Jon
This is a great tip! I’ll remember it…

By: Jon

Jon — Fri, 18 May 2007 17:58:39 +0000

Along the same lines as your way of adding dates, some people have troubles knowing if a month has 31, 30, 28, or 29 days in it. They typically devise elaborate sets of arrays and calculations for number of days in a given month depending on if it’s a leap year, etc.

It’s surprisingly easy to get the info; you just set the following month’s day = 0. 12/0/2007 === 11/30/2007

To find out how many days are in the current month:
[code]
var now = new Date();
now.setMonth(now.getMonth() + 1);
now.setDate(0);
alert(now.getDate());
[/code]

By: John Giotta

John Giotta — Fri, 18 May 2007 14:00:05 +0000

I’ve always found it odd how some developers create an Array of days in a month and may do a leap year check to if position 1 of the array is 28 or 29.

Unless I’m incorrect why not this?
Date.prototype.getMonthDays = function(month) {
var temp_date = new Date(this.getFullYear(), this.getMonth()+1, 1);
temp_date.setDate(temp_date.getDate()-1);
return temp_date.getDate();
};

Works no matter if the year is leap or not. And gets rid of that useless array.

By: K. Adam Christensen

K. Adam Christensen — Sun, 29 Apr 2007 12:38:02 +0000

Since that got cut off, try http://pastie.caboo.se/57443 for the example