Get week of the month
This is an old question, here is my cross-browser solution based on:
- Weeks start on Sunday
- The first week of a month is the one that contains the first of the month
So in March 2013:
- Fri 1 Mar is the first day of week 1
- Sun 3 Mar is the start of week 2
- Sun 31 Mar is the start of week 6 (and is the only day in the that week)
- Mon 1 Apr is the first day of week 1 in April.
Date.prototype.getWeekOfMonth = function(exact) {
var month = this.getMonth()
, year = this.getFullYear()
, firstWeekday = new Date(year, month, 1).getDay()
, lastDateOfMonth = new Date(year, month + 1, 0).getDate()
, offsetDate = this.getDate() + firstWeekday - 1
, index = 1 // start index at 0 or 1, your choice
, weeksInMonth = index + Math.ceil((lastDateOfMonth + firstWeekday - 7) / 7)
, week = index + Math.floor(offsetDate / 7)
;
if (exact || week < 2 + index) return week;
return week === weeksInMonth ? index + 5 : week;
};
// Simple helper to parse YYYY-MM-DD as local
function parseISOAsLocal(s){
var b = s.split(/\D/);
return new Date(b[0],b[1]-1,b[2]);
}
// Tests
console.log('Date Exact|expected not exact|expected');
[ ['2013-02-01', 1, 1],['2013-02-05', 2, 2],['2013-02-14', 3, 3],
['2013-02-23', 4, 4],['2013-02-24', 5, 6],['2013-02-28', 5, 6],
['2013-03-01', 1, 1],['2013-03-02', 1, 1],['2013-03-03', 2, 2],
['2013-03-15', 3, 3],['2013-03-17', 4, 4],['2013-03-23', 4, 4],
['2013-03-24', 5, 5],['2013-03-30', 5, 5],['2013-03-31', 6, 6],
['2013-04-01', 1, 1]
].forEach(function(test){
var d = parseISOAsLocal(test[0])
console.log(test[0] + ' ' +
d.getWeekOfMonth(true) + '|' + test[1] + ' ' +
d.getWeekOfMonth() + '|' + test[2]);
});You don't need to put it directly on the prototype if you don't want to. In my implementation, 6 means "Last", not "Sixth". If you want it to always return the actual week of the month, just pass true.
EDIT: Fixed this to handle 5 & 6-week months. My "unit tests", feel free to fork: http://jsfiddle.net/OlsonDev/5mXF6/1/.
Having struggle with this topic too - thanks to Olson.dev! I've shortened his function a little bit, if somebody is interessted:
// returns week of the month starting with 0
Date.prototype.getWeekOfMonth = function() {
var firstWeekday = new Date(this.getFullYear(), this.getMonth(), 1).getDay();
var offsetDate = this.getDate() + firstWeekday - 1;
return Math.floor(offsetDate / 7);
}
update: if you need a localized version - you have to tweak the firstWeekday variable
// german version - week starts with monday
Date.prototype.getWeekOfMonth = function() {
var firstWeekday = new Date(this.getFullYear(), this.getMonth(), 1).getDay() - 1;
if (firstWeekday < 0) firstWeekday = 6;
var offsetDate = this.getDate() + firstWeekday - 1;
return Math.floor(offsetDate / 7);
}