Click here to Skip to main content
13,556,507 members
Click here to Skip to main content
Add your own
alternative version


67 bookmarked
Posted 16 Jul 2005
Licenced CPOL

JavaScript Date Format

, 3 Dec 2012
Rate this:
Please Sign up or sign in to vote.
A fast VB-like date format function in JavaScript (requires JScript 5.5+).


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.


WOFA, (Without Further Adou):

// a global month names array
var gsMonthNames = new Array(
// a global day names array
var gsDayNames = new Array(
// 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,
            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';


  • 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.



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


About the Author

hector [.j.] rivas
Software Developer (Senior) Ambit Energy
United States United States
I'm an IT solution engineer with extensive experience in software development. I've spearheaded, developed and maintained hardware and software across a myriad of industries including security, construction, and energy, for both the public and private sectors, for non-profit organizations, and for instructional and self-teaching purposes.

With a background in electronics and a passion for tinkering, quality, precision and performance, I've adapted to-and adopted-several technology paradigm changes, from stand-alone and embedded to mobile and the Internet of Things. I've developed microsites, apps and services, and deployed cloud computing systems.

I know several low and high-level programming languages, I'm proficient in several frameworks and I'm at ease adjusting focus from the details to the big picture across the stack-from why to how, and from purpose and value to look and feel.

I'm also a published author and an active blogger.

You may also be interested in...


Comments and Discussions

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 
GeneralRe: A small addition: string 'choose' io switch Pin
Tor2k8-Aug-05 9:30
memberTor2k8-Aug-05 9:30 
GeneralRe: A small addition: string 'choose' io switch Pin
jsc424-Dec-12 22:37
memberjsc424-Dec-12 22:37 

General General    News News    Suggestion Suggestion    Question Question    Bug Bug    Answer Answer    Joke Joke    Praise Praise    Rant Rant    Admin Admin   

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.

Permalink | Advertise | Privacy | Terms of Use | Mobile
Web02-2016 | 2.8.180515.1 | Last Updated 3 Dec 2012
Article Copyright 2005 by hector [.j.] rivas
Everything else Copyright © CodeProject, 1999-2018
Layout: fixed | fluid