Need JS code to find nth weekday of month

Hello:

Many apologies if this is not an appropriate question here... but I have googled my fingers raw and haven't been able to find a script to do what I am looking for. I have little experience with JavaScript.

I have a VBA script (code at the end of this post) that returns the date corresponding to a given occurrence of a given weekday, e.g. Ask it for the 3rd Tuesday in October 2012 and it gives you 16-OCT-2012. It defaults to current year if you don't pass the Year argument.

It's a pretty simple script, but I need to either finds something in JavaScript that does the same thing, or convert the VBA code to JavaScript. I can't help but think that many people have already written scripts that do this. Any chance someone can lead me in a productive direction here?

Regards,

Steve Jones

(update - I noticed the code didn't retain its formatting, so I attached a text file)

-begin VBA code-
Public Function xdate(m As Integer, n As Integer, wd As Integer, Optional y As Integer = 0) As Date
'// m = 1-12 (Jan-Dec), n = 1-5 (1st-4th, last), wd = 1-7 (Sun-Sat), y = 1900-9999 or left blank for current year
Select Case y
Case 0 ' // Default. Use the current year.
y = year(Date)
Case 1900 To 9999 ' // treat the value as an explicit year
Case -100 To -1, 1 To 100 ' // treat the value as an offset to be applied to the current year
y = year(Date) + y
Case Else
' // invalid value. Insert whatever error processing you like.
End Select
Select Case n
Case 1 To 4 '// first through fourth
Case 5 '// last. We need to check to see it fell within the month specified, if not, use 4.
xdate = DateSerial(y, m, (8 - weekday(DateSerial(y, m, 1), (wd + 1) Mod 8)) + ((n - 1) * 7))
If month(xdate) <> m Then
n = 4
End If
Case Else
' // invalid value - insert error processing code here if you like.
' // Probably should check the other arguments as well.
End Select
xdate = DateSerial(y, m, (8 - weekday(DateSerial(y, m, 1), (wd + 1) Mod 8)) + ((n - 1) * 7))
End Function
-end vba code-

Try
var getDate = function(index,weekday,month,year){
// index what occurence of the weekday we look for (1 and upwards)
// weekday 0-6 (= Sunday - Monday)
// month 1-12 (= January - December) optional defaults to current month
// year (a four digit number) optional defaults to current year
var now = new Date(), co = 1, result;
month = month || now.getMonth() + 1;
year = year || now.getFullYear();
do {
result = new Date(year,month-1,co);
result.getDay() == weekday && index--;
co++;
}
while (index > 0);
return result
};

Or, if you want an "error" if the index is not within the month (seems that's what your VB Script does), this will return false when "out of range":

var getDate = function(index,weekday,month,year){
// index what occurence of the weekday we look for (1 and upwards)
// weekday 0-6 (= Sunday - Monday)
// month 1-12 (= January - December) optional defaults to current month
// year (a four digit number) optional defaults to current year
var now = new Date(), co = 1, result;
month = month || now.getMonth() + 1;
year = year || now.getFullYear();
do {
result = new Date(year,month-1,co);
result.getDay() == weekday && index--;
if(result.getMonth() + 1 != month || index + co < 2){return false};
co++;
}
while (index > 0);
return result
};

I just wanted to practise my brains :) I am not sure that the requested feature is frquently used that so you could not find the good implementation both javascript or others.

Let's consider your issue from another point of view. There are many coupled methods named as setXXX/getXXX (for example, setDate/getDate to set and get the day number in month). But having the getDay method (to retrieve the weekday of the date) we do not have setDay to set it. So let's try to implement it. We will pass the day of the week as a mandatory argument and the optional number of the wek in the month. I have put many comments to describe what happens there in detail. Feel free to squeeze the code deleting them.



/**
* Sets the day of the week value of the Date object using local time.
*
* The weekday is an integer between 0 and 6 representing the day of
* the week and corresponds to the day of the week as follows:
* 0 - Sunday
* 1 - Monday
* 2 - Tuesday
* 3 - Wednesday
* 4 - Thurday
* 5 - Friday
* 6 - Saturday
*
* If the second argument is defined then it sets to the week number
* when this day of the week occurs. It is the number of the week
* (the first week of the month is 0).
*
* @param Integer Required. A numeric value of the day of the week.
* @param Integer Optional. A numeric value of the week of the month.
* @param Date
* @access public
*/
Date.prototype.setDay = function(w, n)
{
// Get the reference to the Date object
var x = this;
// Set the date to the first day of the month
x.setDate(1);
// Calculate the distance to the nearest required weekday
var d = w - x.getDay() + 1;
if ( d < 0 ) {
d += 7;
}
// Calculate the date corresponding to the required weekday
d += (n || 0) * 7;
// Set the date and return the result as all methods do
return x.setDate(d);
};

for (var i = 1; i <= 31; i++) {
var x = new Date(2012, 9, i);

// Set 3rd Tuesday in October 2012
var y = new Date(2012, 9, i);
y.setDay(2, 2);

alert([x, y]);
}