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I have to admit, Microsoft Ajax JavaScript library is not so well known and popular these days. But still if offers a lot of functionalities a developer might use doing some client side work. I believe can be very useful for SharePoint developers, as SharePoint, being a web forms based technology, use it.

For this article, my objective is to explain a little bit more about Ajax Date type extensions, which are a set of methods designed to extend JavaScript built-in Date object.

Format date as string

Converting a date object to a formatted string has never been easier. Ajax is adding a extension method to Date object called “format” which accepts a format string as parameter. As rule this string should contain the following placeholders to show different parts of the date:

  • yyyy – show full year
  • yy – show short format of year (only the last 2 numbers)
  • M – show short month number (doesn’t add leading zero if month number is under 10)
  • MM – show month
  • MMM – show month name, like Oct, Jan
  • MMM – show full month name, like October and January
  • d – show short day number (doesn’t add leading zero if day number is under 10)
  • dd – show day
  • ddd – show day name, like Sat, Sun….
  • dddd – show full day name, like Saturday or Sunday
  • hh- show hours
  • mm – show minutes
  • ss- show seconds
var dt = new Date();

// 2015-10-22T09:18:30Z
dt.format("yyyy-MM-ddThh:mm:ttZ") 

// 2015/10/22
dt.format("yyyy/MM/dd");

// 22-Oct-15
dt.format("dd-MMM-yy");

// Output Thu
dt.format("ddd");

// Output Thursday
dt.format("dddd");

// Output October
dt.format("MMMM");

You can play with this format string parameter and find more date formats. There is not rocket science here and it is straight format.

Convert a formatted string to Date

Let’s now discussed about the reverse process to convert a string to Date object. Microsoft implemented a static method for Date object called “parseInvariant”. It returns a date if string is a valid representation of it, otherwise returns null.

// @value = A string that represents a date.
// @format = A string provided the format information. For me an array of strings did not work, even  Microsoft says this is the correct parameter type
 var a = Date.parseInvariant(value, format);

You can see below some examples.

var dt;

// This is valid date and is 1st of december 2015. 
dt = "2015-12-01";
Date.parseInvariant(dt,"yyyy-MM-dd");
dt = "12/01/2015";
Date.parseInvariant(dt,"dd/MM/yyyy");
dt = "01 December 2015";
Date.parseInvariant(dt,"dd MMMM yyyy");

It seems for “parseInvariant” function we use the same placeholders like we used for “format” function.

The functions I have talked about do not depend on the culture, but there are also other two versions which are affected by it: “parseLocale” and “localeFormat”. Documentation about entire Date type extended methods can be found here. I have to admit Microsoft did not provide too much details about this, but I hope my findings will help you work smarter doing client side development on web forms based technology (not only, because Ajax is not depending on server side).

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