Calculate the correct week number for weeks starting at any date. #4857

http://en.wikipedia.org/wiki/ISO_week

Contributed by Holger Just

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@3789 e93f8b46-1217-0410-a6f0-8f06a7374b81
This commit is contained in:
Eric Davis 2010-06-19 22:52:09 +00:00
parent 093853b56a
commit b2e903ff7c
1 changed files with 20 additions and 8 deletions

View File

@ -1694,15 +1694,27 @@ Date.prototype.getDayOfYear = function() {
return Math.floor(time / Date.DAY);
};
/** Returns the number of the week in year, as defined in ISO 8601. */
/** Returns the number of the week in year, as defined in ISO 8601.
This function is only correct if `this` is the first day of the week. */
Date.prototype.getWeekNumber = function() {
var d = new Date(this.getFullYear(), this.getMonth(), this.getDate(), 0, 0, 0);
var DoW = d.getDay();
d.setDate(d.getDate() - (DoW + 6) % 7 + 3); // Nearest Thu
var ms = d.valueOf(); // GMT
d.setMonth(0);
d.setDate(4); // Thu in Week 1
return Math.round((ms - d.valueOf()) / (7 * 864e5)) + 1;
var d = new Date(this.getFullYear(), this.getMonth(), this.getDate());
var days = 1000*60*60*24; // one day in milliseconds
// get the thursday of the current week
var this_thursday = new Date(
d.valueOf() // selected date
- (d.getDay() % 7)*days // previous sunday
+ 4*days // + 4 days
).valueOf();
// the thursday in the first week of the year
var first_thursday = new Date(
new Date(this.getFullYear(), 0, 4).valueOf() // January 4 is in the first week by definition
- (d.getDay() % 7)*days // previous sunday
+ 4*days // + 4 days
).valueOf();
return Math.round((this_thursday - first_thursday) / (7*days)) + 1;
};
/** Checks date and time equality */