jsDate

VBScript and VB6 native Date functions emulated in Javascript

About

As a scripting language, Javascript (aka ECMAScript, aka JScript) is extremely powerful, but quite weak with date/time manipulation.  Several types of date/time operations are very difficult to accomplish (and accurately) in Javascript.  VBScript is comparatively very strong in that area, though, with several intrinsic date/time-related functions, like IsDate, CDate, DateAdd, DateDiff, DatePart, MonthName, WeekdayName, and FormatDateTime.  Better yet is VB6's Format function. 

Anyway, after banging my head on the wall for the nth time, I decided to try to re-create those functions in a Javascript include file, called jsDate.  Try it out...

Live Demo (element relationships: related,  active )

3) and get this Result:

Source (right-click and save)

notes

• IsDate, DateAdd, and DateDiff are the biggest helps for Javascript.  The rest are icing.
• Compatibility: the functions should work in any modern browser.  The demo itself works in IE and Firefox at least.
• Usage: copy the file to your project, link to it, and you can begin using the functions just as in VBScript.
• Limitations: in VBScript, DateDiff and DatePart() accept the option parameter FirstWeekOfYear.  jsDate ignores this, and assumes Sunday & the week of January 1st (which are VBScript's defaults).
• Enhancements: jsDate's DateAdd and DateDiff functions can track Milliseconds (unlike VBScript).  I've also added a Format function emulating the same in VB6 (date-features only).  This should fill the gaps in FormatDateTime (which wraps Format anyway).
• Other differences: jsDate's IsDate has different tolerances than VBScript's.  It allows otherwise invalid date values through (Javascript internally "corrects" the date, e.g. 1/32/2000 → 2/1/2000), but disallows other date formats which VBScript accepts (e.g. yearless dates, dateless time, and dash or dot date separators).  I added the new CDate implementation for this reason.
• It turns out that VBScript's DateDiff does not check that each YYYY, M, or Q interval has been completed, but just if it has rolled over into a new one.  So in VBScript, DateDiff("yyyy", "12/31/2000", "1/1/2001") returns 1 (even though it's just 1 day completed, not a year).  As of v0.94, jsDate's DateDiff now behaves this way too.  One exception is the Q interval, which still checks for 3 months completed (does anyone really use Q?).
• maybe TODO: better documentation; make jsDate's IsDate tolerances more like VBScript's; implement FirstWeekOfYear parameter; implement Now; implement DateSerial/DateValue/Time/TimeSerial/TimeValue?;

history

• 2024-05-09 - v2024-05-09: (been long enough?)
  • CDate: if no time specified, assumes midnight (otherwise JS presumes UTC timezone and offsets everything)
    (thanks for the heads-up, Barry Koehler)
• 2018-10-09 - v2018-10-09: (been long enough?)
  • Format: fixed "mm" token to properly pad
  • IsDate: return false for null (unlike Javascript, which bizarrely returns the epoch for new Date(null))
• 2006-03-28 - v1.00 b1:
  • added MonthNames and WeekdayNames arrays
  • added FormatDateTime w/US defaults
  • added VB6's Format, for better non-US flexibility
  • changed functions to methods of intrinsic Date object
  • changed DateDiff to now accept yearless date params, like VBS
  • implemented CDate (can handle dash/dot date separators, yearless dates, dateless times & other variations)
  • implemented DateDiff/"ww" interval
  • implemented FirstDayOfWeek parameter on DateDiff, DatePart, WeekdayName, and Format
  • fixed DatePart/"y", "w", & "ww" intervals
  • fixed DateDiff/"w" interval (caught by Michael Leibman)
  • fixed DateDiff/DST rollover (thanks to Roger Dear for the heads-up & Michael Leibman for suggesting a fix)
  • fixed MonthName & WeekdayName params to match VBS (now accept number, but dates still work for compatibility)
• 2005-08-04 - v0.94:
  • scrapped 0.93b's new DateDiff interval code to better match VBScript's simplistic approach
• 2005-08-03 - v0.93b:
  • fixed DateDiff/leapyear bug with "yyyy", "m", & "q" intervals (thanks Rolando and Dr. John for catching this)
• 2004-11-26 - v0.91:
  • fixed DatePart/"ww" bug
  • added WeekdayName & MonthName
  • first published
• 2004-08-30 - v0.9:
  • brand new

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credits/author

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