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JavaScript Date Format

, 3 Dec 2012 CPOL 226.7K 66
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A fast VB-like date format function in JavaScript (requires JScript 5.5+).

Introduction

I needed a JavaScript date format function such as the Visual Basic Format function, in which you can pass a format string; my first approach was to issue a series of consecutive and "destructive" replace calls, but upon discovering that the 5.5 (or higher) version of JScript supported the use of a function as the replaceText argument of the replace method, I got creative.

Here's an example call of what I wanted:

SomeDiv.innerText = (new Date()).format('dddd, mmmm dd, yyyy.');

This would display:

Saturday, July 16, 2005

So in my first approach, I globally and case-insensitively replaced dddd with the corresponding string, which "destroyed" every occurrence, so that later in the code I could replace dd with the date number.

This worked just fine, but I knew that by inspecting the format specifier for a match, I could skip the search of every format specifier; say I only want the month and the date; well, by switching upon the format specifier (or rather "datepart" specifier), the year replacement will never be issued. Get it?

The fun part relies in the use of a function in the replaceText argument of the replace method; this way the $1 property as a function argument always represents the last match.

Other considerations include the format or "datepart" specifiers: none other than yyyy will be parsed as the year; months and days have the usual three flavors of fullname (mmmm), three-letter (mmm) or numeric (mm); hours (hh) can be rectified to the 12-hour format with the a/p specifier, and minutes (nn) and seconds (ss) may also be specified.

Implementation

WOFA, (Without Further Adou):

// a global month names array
var gsMonthNames = new Array(
'January',
'February',
'March',
'April',
'May',
'June',
'July',
'August',
'September',
'October',
'November',
'December'
);
// a global day names array
var gsDayNames = new Array(
'Sunday',
'Monday',
'Tuesday',
'Wednesday',
'Thursday',
'Friday',
'Saturday'
);
// the date format prototype
Date.prototype.format = function(f)
{
    if (!this.valueOf())
        return ' ';

    var d = this;

    return f.replace(/(yyyy|mmmm|mmm|mm|dddd|ddd|dd|hh|nn|ss|a\/p)/gi,
        function($1)
        {
            switch ($1.toLowerCase())
            {
            case 'yyyy': return d.getFullYear();
            case 'mmmm': return gsMonthNames[d.getMonth()];
            case 'mmm':  return gsMonthNames[d.getMonth()].substr(0, 3);
            case 'mm':   return (d.getMonth() + 1).zf(2);
            case 'dddd': return gsDayNames[d.getDay()];
            case 'ddd':  return gsDayNames[d.getDay()].substr(0, 3);
            case 'dd':   return d.getDate().zf(2);
            case 'hh':   return ((h = d.getHours() % 12) ? h : 12).zf(2);
            case 'nn':   return d.getMinutes().zf(2);
            case 'ss':   return d.getSeconds().zf(2);
            case 'a/p':  return d.getHours() < 12 ? 'a' : 'p';
            }
        }
    );
}

Notes

  • A date with a value of 0 returns a non-breaking space.
  • Notice how the d variable is available to the replacement function (but the this object is not).
  • The zf number prototype can be found in Extending JavaScript Objects with Prototypes, where it is called 'zp' for zero padding. It pads a number with zeroes the specified number of times, up to the number's character length, i.e. 2 turns into 02, but 16 remains 16.
  • The regular expression looks for any of the bracketed pattern characters in a two+ sequence, or for the very specific a/p match.
  • Defining names globally helps and serves other purposes, i.e. listing days in a calendar.

Enjoy.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

hector [.j.] rivas
Software Developer (Senior) Code Authority, Inc.
United States United States
Pride in craftsmanship is my new thing.

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Comments and Discussions

 
Questionfor month part if u put mmm it is returning 000 Pin
Keerthi Kumar(Andar)16-Apr-15 0:24
memberKeerthi Kumar(Andar)16-Apr-15 0:24 
GeneralMy vote of 5 Pin
Niral Soni29-Jan-13 5:34
memberNiral Soni29-Jan-13 5:34 
GeneralMy vote of 4 Pin
Mario Majčica3-Dec-12 3:40
memberMario Majčica3-Dec-12 3:40 
GeneralRe: My vote of 4 Pin
hector.j.rivas3-Dec-12 4:18
memberhector.j.rivas3-Dec-12 4:18 
GeneralRe: My vote of 4 Pin
Mario Majčica3-Dec-12 4:21
memberMario Majčica3-Dec-12 4:21 
GeneralRe: My vote of 4 Pin
hector.j.rivas3-Dec-12 4:27
memberhector.j.rivas3-Dec-12 4:27 
GeneralPutting it all together so far Pin
murray562-Mar-07 16:15
membermurray562-Mar-07 16:15 
GeneralRe: Putting it all together so far Pin
murray562-Mar-07 17:09
membermurray562-Mar-07 17:09 
GeneralRe: Putting it all together so far Pin
Tor2k4-Mar-07 20:09
memberTor2k4-Mar-07 20:09 
GeneralRe: Putting it all together so far Pin
murray565-Mar-07 21:49
membermurray565-Mar-07 21:49 
Generalhey Pin
Frenaaa3-Dec-06 8:09
memberFrenaaa3-Dec-06 8:09 
GeneralRe: hey Pin
Tor2k8-Dec-06 7:22
memberTor2k8-Dec-06 7:22 
GeneralEasy but useful Pin
Ninghuan25-Apr-06 22:01
memberNinghuan25-Apr-06 22:01 
GeneralC#-like formats Pin
Kjetil Klaussen8-Mar-06 23:15
memberKjetil Klaussen8-Mar-06 23:15 
GeneralZF Pin
Tunez1-Aug-05 1:09
memberTunez1-Aug-05 1:09 
GeneralRe: ZF Pin
Tor2k2-Aug-05 14:00
memberTor2k2-Aug-05 14:00 
GeneralA couple of bugs Pin
Richard Deeming26-Jul-05 7:08
memberRichard Deeming26-Jul-05 7:08 
GeneralRe: A couple of bugs Pin
Tor2k26-Jul-05 10:42
memberTor2k26-Jul-05 10:42 
GeneralRe: A small addition Pin
Dougww5-Aug-05 3:13
memberDougww5-Aug-05 3:13 
GeneralRe: A small addition Pin
Tor2k6-Aug-05 7:16
memberTor2k6-Aug-05 7:16 
GeneralRe: A small addition Pin
Richard Deeming10-Aug-05 2:21
memberRichard Deeming10-Aug-05 2:21 
GeneralRe: A small addition Pin
Tor2k10-Aug-05 6:18
memberTor2k10-Aug-05 6:18 
GeneralRe: A small addition Pin
shadowcreeper20-Apr-09 10:05
membershadowcreeper20-Apr-09 10:05 
GeneralRe: A small addition Pin
Tor2k21-Apr-09 5:47
memberTor2k21-Apr-09 5:47 
If it works, that's fine!

I would save some d.getDate() calls by setting up a variable, though. Not that users will notice, but programmers should!

There is no spoon.

GeneralRe: A small addition: string 'choose' io switch Pin
Tor2k8-Aug-05 9:30
memberTor2k8-Aug-05 9:30 

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