jsDate: VBScript native Date functions emulated for Javascript

/*
Name: jsDate
Desc: VBScript native Date functions emulated for Javascript
Author: Rob Eberhardt, Slingshot Solutions - http://slingfive.com/
Note: see jsDate.txt for more info
*/

// constants
vbGeneralDate=0; vbLongDate=1; vbShortDate=2; vbLongTime=3; vbShortTime=4;  // NamedFormat
vbUseSystemDayOfWeek=0; vbSunday=1; vbMonday=2; vbTuesday=3; vbWednesday=4; vbThursday=5; vbFriday=6; vbSaturday=7; // FirstDayOfWeek
vbUseSystem=0; vbFirstJan1=1; vbFirstFourDays=2; vbFirstFullWeek=3; // FirstWeekOfYear

// arrays (1-based)
Date.MonthNames = [null,'January','February','March','April','May','June','July','August','September','October','November','December'];
Date.WeekdayNames = [null,'Sunday','Monday','Tuesday','Wednesday','Thursday','Friday','Saturday'];




Date.IsDate = function(p_Expression){
 return !isNaN(new Date(p_Expression));  // <-- review further
}

Date.CDate = function(p_Date){
 if(Date.IsDate(p_Date)){ return new Date(p_Date); }

 var strTry = p_Date.replace(/\-/g, '/').replace(/\./g, '/').replace(/ /g, '/'); // fix separators
 strTry = strTry.replace(/pm$/i, " pm").replace(/am$/i, " am"); // and meridian spacing
 if(Date.IsDate(strTry)){ return new Date(strTry); }

 var strTryYear = strTry + '/' + new Date().getFullYear(); // append year
 if(Date.IsDate(strTryYear)){ return new Date(strTryYear); }
 

 if(strTry.indexOf(":")){ // if appears to have time
  var strTryYear2 = strTry.replace(/ /, '/' + new Date().getFullYear() + ' '); // insert year
  if(Date.IsDate(strTryYear2)){ return new Date(strTryYear2); }

  var strTryDate = new Date().toDateString() + ' ' + p_Date; // pre-pend current date
  if(Date.IsDate(strTryDate)){ return new Date(strTryDate); }
 }
 
 return false; // double as looser IsDate
 //throw("Error #13 - Type mismatch"); // or is this better? 
}
 


Date.DateAdd = function(p_Interval, p_Number, p_Date){
 if(!Date.CDate(p_Date)){ return "invalid date: '" + p_Date + "'"; }
 if(isNaN(p_Number)){ return "invalid number: '" + p_Number + "'"; } 

 p_Number = new Number(p_Number);
 var dt = Date.CDate(p_Date);
 
 switch(p_Interval.toLowerCase()){
  case "yyyy": {
   dt.setFullYear(dt.getFullYear() + p_Number);
   break;
  }
  case "q": {
   dt.setMonth(dt.getMonth() + (p_Number*3));
   break;
  }
  case "m": {
   dt.setMonth(dt.getMonth() + p_Number);
   break;
  }
  case "y":   // day of year
  case "d":   // day
  case "w": {  // weekday
   dt.setDate(dt.getDate() + p_Number);
   break;
  }
  case "ww": { // week of year
   dt.setDate(dt.getDate() + (p_Number*7));
   break;
  }
  case "h": {
   dt.setHours(dt.getHours() + p_Number);
   break;
  }
  case "n": {  // minute
   dt.setMinutes(dt.getMinutes() + p_Number);
   break;
  }
  case "s": {
   dt.setSeconds(dt.getSeconds() + p_Number);
   break;
  }
  case "ms": { // JS extension
   dt.setMilliseconds(dt.getMilliseconds() + p_Number);
   break;
  }
  default: {
   return "invalid interval: '" + p_Interval + "'";
  }
 }
 return dt;
}



Date.DateDiff = function(p_Interval, p_Date1, p_Date2, p_FirstDayOfWeek){
 if(!Date.CDate(p_Date1)){ return "invalid date: '" + p_Date1 + "'"; }
 if(!Date.CDate(p_Date2)){ return "invalid date: '" + p_Date2 + "'"; }
 p_FirstDayOfWeek = (isNaN(p_FirstDayOfWeek) || p_FirstDayOfWeek==0) ? vbSunday : parseInt(p_FirstDayOfWeek); // set default & cast

 var dt1 = Date.CDate(p_Date1);
 var dt2 = Date.CDate(p_Date2);

 // correct DST-affected intervals ("d" & bigger)
 if("h,n,s,ms".indexOf(p_Interval.toLowerCase())==-1){
  if(p_Date1.toString().indexOf(":") ==-1){ dt1.setUTCHours(0,0,0,0) }; // no time, assume 12am
  if(p_Date2.toString().indexOf(":") ==-1){ dt2.setUTCHours(0,0,0,0) }; // no time, assume 12am
 }


 // get ms between UTC dates and make into "difference" date
 var iDiffMS = dt2.valueOf() - dt1.valueOf();
 var dtDiff = new Date(iDiffMS);

 // calc various diffs
 var nYears  = dt2.getUTCFullYear() - dt1.getUTCFullYear();
 var nMonths = dt2.getUTCMonth() - dt1.getUTCMonth() + (nYears!=0 ? nYears*12 : 0);
 var nQuarters = parseInt(nMonths / 3); //<<-- different than VBScript, which watches rollover not completion
 
 var nMilliseconds = iDiffMS;
 var nSeconds = parseInt(iDiffMS / 1000);
 var nMinutes = parseInt(nSeconds / 60);
 var nHours = parseInt(nMinutes / 60);
 var nDays  = parseInt(nHours / 24); // <-- now fixed for DST switch days
 var nWeeks = parseInt(nDays / 7);


 if(p_Interval.toLowerCase()=='ww'){
   // set dates to 1st & last FirstDayOfWeek
   var offset = Date.DatePart("w", dt1, p_FirstDayOfWeek)-1;
   if(offset){ dt1.setDate(dt1.getDate() +7 -offset); }
   var offset = Date.DatePart("w", dt2, p_FirstDayOfWeek)-1;
   if(offset){ dt2.setDate(dt2.getDate() -offset); }
   // recurse to "w" with adjusted dates
   var nCalWeeks = Date.DateDiff("w", dt1, dt2) + 1;
 }
 // TODO: similar for 'w'?
 
 
 // return difference
 switch(p_Interval.toLowerCase()){
  case "yyyy": return nYears;
  case "q": return nQuarters;
  case "m": return nMonths;
  case "y":   // day of year
  case "d": return nDays;
  case "w": return nWeeks;
  case "ww":return nCalWeeks; // week of year 
  case "h": return nHours;
  case "n": return nMinutes;
  case "s": return nSeconds;
  case "ms":return nMilliseconds; // not in VBScript
  default : return "invalid interval: '" + p_Interval + "'";
 }
}




Date.DatePart = function(p_Interval, p_Date, p_FirstDayOfWeek){
 if(!Date.CDate(p_Date)){ return "invalid date: '" + p_Date + "'"; }

 var dtPart = Date.CDate(p_Date);
 
 switch(p_Interval.toLowerCase()){
  case "yyyy": return dtPart.getFullYear();
  case "q": return parseInt(dtPart.getMonth() / 3) + 1;
  case "m": return dtPart.getMonth() + 1;
  case "y": return Date.DateDiff("y", "1/1/" + dtPart.getFullYear(), dtPart) + 1; // day of year
  case "d": return dtPart.getDate();
  case "w": return Date.Weekday(dtPart.getDay()+1, p_FirstDayOfWeek);  // weekday
  case "ww":return Date.DateDiff("ww", "1/1/" + dtPart.getFullYear(), dtPart, p_FirstDayOfWeek) + 1; // week of year
  case "h": return dtPart.getHours();
  case "n": return dtPart.getMinutes();
  case "s": return dtPart.getSeconds();
  case "ms":return dtPart.getMilliseconds(); // <-- JS extension, NOT in VBScript
  default : return "invalid interval: '" + p_Interval + "'";
 }
}



Date.MonthName = function(p_Month, p_Abbreviate){
 if(isNaN(p_Month)){ // v0.94- compat: extract real param from passed date
  if(!Date.CDate(p_Month)){ return "invalid month: '" + p_Month + "'"; }
  p_Month = DatePart("m", Date.CDate(p_Month));
 }

 var retVal = Date.MonthNames[p_Month];
 if(p_Abbreviate==true){ retVal = retVal.substring(0, 3) } // abbr to 3 chars
 return retVal;
}


Date.WeekdayName = function(p_Weekday, p_Abbreviate, p_FirstDayOfWeek){
 if(isNaN(p_Weekday)){ // v0.94- compat: extract real param from passed date
  if(!Date.CDate(p_Weekday)){ return "invalid weekday: '" + p_Weekday + "'"; }
  p_Weekday = DatePart("w", Date.CDate(p_Weekday));
 }
 p_FirstDayOfWeek = (isNaN(p_FirstDayOfWeek) || p_FirstDayOfWeek==0) ? vbSunday : parseInt(p_FirstDayOfWeek); // set default & cast

 var nWeekdayNameIdx = ((p_FirstDayOfWeek-1 + parseInt(p_Weekday)-1 +7) % 7) + 1; // compensate nWeekdayNameIdx for p_FirstDayOfWeek
 var retVal = Date.WeekdayNames[nWeekdayNameIdx];
 if(p_Abbreviate==true){ retVal = retVal.substring(0, 3) } // abbr to 3 chars
 return retVal;
}


// adjusts weekday for week starting on p_FirstDayOfWeek
Date.Weekday=function(p_Weekday, p_FirstDayOfWeek){ 
 p_FirstDayOfWeek = (isNaN(p_FirstDayOfWeek) || p_FirstDayOfWeek==0) ? vbSunday : parseInt(p_FirstDayOfWeek); // set default & cast

 return ((parseInt(p_Weekday) - p_FirstDayOfWeek +7) % 7) + 1;
}





Date.FormatDateTime = function(p_Date, p_NamedFormat){
 if(p_Date.toUpperCase().substring(0,3) == "NOW"){ p_Date = new Date() };
 if(!Date.CDate(p_Date)){ return "invalid date: '" + p_Date + "'"; }
 if(isNaN(p_NamedFormat)){ p_NamedFormat = vbGeneralDate };

 var dt = Date.CDate(p_Date);

 switch(parseInt(p_NamedFormat)){
  case vbGeneralDate: return dt.toString();
  case vbLongDate:  return Format(p_Date, 'DDDD, MMMM D, YYYY');
  case vbShortDate:  return Format(p_Date, 'MM/DD/YYYY');
  case vbLongTime:  return dt.toLocaleTimeString();
  case vbShortTime:  return Format(p_Date, 'HH:MM:SS');
  default: return "invalid NamedFormat: '" + p_NamedFormat + "'";
 }
}


Date.Format = function(p_Date, p_Format, p_FirstDayOfWeek, p_firstweekofyear) {
 if(!Date.CDate(p_Date)){ return "invalid date: '" + p_Date + "'"; }
 if(!p_Format || p_Format==''){ return dt.toString() };

 var dt = Date.CDate(p_Date);

 // Zero-padding formatter
 this.pad = function(p_str){
  if(p_str.toString().length==1){p_str = '0' + p_str}
  return p_str;
 }

 var ampm = dt.getHours()>=12 ? 'PM' : 'AM'
 var hr = dt.getHours();
 if (hr == 0){hr = 12};
 if (hr > 12) {hr -= 12};
 var strShortTime = hr +':'+ this.pad(dt.getMinutes()) +':'+ this.pad(dt.getSeconds()) +' '+ ampm;
 var strShortDate = (dt.getMonth()+1) +'/'+ dt.getDate() +'/'+ new String( dt.getFullYear() ).substring(2,4);
 var strLongDate = Date.MonthName(dt.getMonth()+1) +' '+ dt.getDate() +', '+ dt.getFullYear();  //

 var retVal = p_Format;
 
 // switch tokens whose alpha replacements could be accidentally captured
 retVal = retVal.replace( new RegExp('C', 'gi'), 'CCCC' ); 
 retVal = retVal.replace( new RegExp('mmmm', 'gi'), 'XXXX' );
 retVal = retVal.replace( new RegExp('mmm', 'gi'), 'XXX' );
 retVal = retVal.replace( new RegExp('dddddd', 'gi'), 'AAAAAA' ); 
 retVal = retVal.replace( new RegExp('ddddd', 'gi'), 'AAAAA' ); 
 retVal = retVal.replace( new RegExp('dddd', 'gi'), 'AAAA' );
 retVal = retVal.replace( new RegExp('ddd', 'gi'), 'AAA' );
 retVal = retVal.replace( new RegExp('timezone', 'gi'), 'ZZZZ' );
 retVal = retVal.replace( new RegExp('time24', 'gi'), 'TTTT' );
 retVal = retVal.replace( new RegExp('time', 'gi'), 'TTT' );

 // now do simple token replacements
 retVal = retVal.replace( new RegExp('yyyy', 'gi'), dt.getFullYear() );
 retVal = retVal.replace( new RegExp('yy', 'gi'), new String( dt.getFullYear() ).substring(2,4) );
 retVal = retVal.replace( new RegExp('y', 'gi'), Date.DatePart("y", dt) );
 retVal = retVal.replace( new RegExp('q', 'gi'), Date.DatePart("q", dt) );
 retVal = retVal.replace( new RegExp('mm', 'gi'), (dt.getMonth() + 1) ); 
 retVal = retVal.replace( new RegExp('m', 'gi'), (dt.getMonth() + 1) ); 
 retVal = retVal.replace( new RegExp('dd', 'gi'), this.pad(dt.getDate()) );
 retVal = retVal.replace( new RegExp('d', 'gi'), dt.getDate() );
 retVal = retVal.replace( new RegExp('hh', 'gi'), this.pad(dt.getHours()) );
 retVal = retVal.replace( new RegExp('h', 'gi'), dt.getHours() );
 retVal = retVal.replace( new RegExp('nn', 'gi'), this.pad(dt.getMinutes()) );
 retVal = retVal.replace( new RegExp('n', 'gi'), dt.getMinutes() );
 retVal = retVal.replace( new RegExp('ss', 'gi'), this.pad(dt.getSeconds()) ); 
 retVal = retVal.replace( new RegExp('s', 'gi'), dt.getSeconds() ); 
 retVal = retVal.replace( new RegExp('t t t t t', 'gi'), strShortTime ); 
 retVal = retVal.replace( new RegExp('am/pm', 'g'), dt.getHours()>=12 ? 'pm' : 'am');
 retVal = retVal.replace( new RegExp('AM/PM', 'g'), dt.getHours()>=12 ? 'PM' : 'AM');
 retVal = retVal.replace( new RegExp('a/p', 'g'), dt.getHours()>=12 ? 'p' : 'a');
 retVal = retVal.replace( new RegExp('A/P', 'g'), dt.getHours()>=12 ? 'P' : 'A');
 retVal = retVal.replace( new RegExp('AMPM', 'g'), dt.getHours()>=12 ? 'pm' : 'am');
 // (always proceed largest same-lettered token to smallest)

 // now finish the previously set-aside tokens 
 retVal = retVal.replace( new RegExp('XXXX', 'gi'), Date.MonthName(dt.getMonth()+1, false) ); //
 retVal = retVal.replace( new RegExp('XXX',  'gi'), Date.MonthName(dt.getMonth()+1, true ) ); //
 retVal = retVal.replace( new RegExp('AAAAAA', 'gi'), strLongDate ); 
 retVal = retVal.replace( new RegExp('AAAAA', 'gi'), strShortDate ); 
 retVal = retVal.replace( new RegExp('AAAA', 'gi'), Date.WeekdayName(dt.getDay()+1, false, p_FirstDayOfWeek) ); // 
 retVal = retVal.replace( new RegExp('AAA',  'gi'), Date.WeekdayName(dt.getDay()+1, true,  p_FirstDayOfWeek) ); // 
 retVal = retVal.replace( new RegExp('TTTT', 'gi'), dt.getHours() + ':' + this.pad(dt.getMinutes()) );
 retVal = retVal.replace( new RegExp('TTT',  'gi'), hr +':'+ this.pad(dt.getMinutes()) +' '+ ampm );
 retVal = retVal.replace( new RegExp('CCCC', 'gi'), strShortDate +' '+ strShortTime ); 

 // finally timezone
 tz = dt.getTimezoneOffset();
 timezone = (tz<0) ? ('GMT-' + tz/60) : (tz==0) ? ('GMT') : ('GMT+' + tz/60);
 retVal = retVal.replace( new RegExp('ZZZZ', 'gi'), timezone );

 return retVal;
}



// ====================================

/* if desired, map new methods to direct functions
*/
IsDate = Date.IsDate;
CDate = Date.CDate;
DateAdd = Date.DateAdd;
DateDiff = Date.DateDiff;
DatePart = Date.DatePart;
MonthName = Date.MonthName;
WeekdayName = Date.WeekdayName;
Weekday = Date.Weekday;
FormatDateTime = Date.FormatDateTime;
Format = Date.Format;



/* and other capitalizations for easier porting
isDate = IsDate;
dateAdd = DateAdd;
dateDiff = DateDiff;
datePart = DatePart;
monthName = MonthName;
weekdayName = WeekdayName;
formatDateTime = FormatDateTime;
format = Format;

isdate = IsDate;
dateadd = DateAdd;
datediff = DateDiff;
datepart = DatePart;
monthname = MonthName;
weekdayname = WeekdayName;
formatdatetime = FormatDateTime;

ISDATE = IsDate;
DATEADD = DateAdd;
DATEDIFF = DateDiff;
DATEPART = DatePart;
MONTHNAME = MonthName;
WEEKDAYNAME = WeekdayName;
FORMATDATETIME = FormatDateTime;
FORMAT = Format;
*/