I’m working on an expenses application. In order to do it, I need to display the entire month, with full weeks in each (from Saturday to Friday).
To do this, I need to know what date the Saturday in the first week falls, and the date of the first Saturday in the following month.
Here’s the code (assuming year is a 4-digit year, and month is a 1-12 number):
// { start date
var start=new Date(year, month-1, 1);
var day=start.getDay();
day=(day+1)%7;
start=new Date(start-3600000*24*day);
// }
// { end date
month++;
if (month==13) {
month=1;
year++;
}
var end=new Date(year, month-1, 1);
var day=end.getDay();
day=7-((day+1)%7);
end=new Date((+end)+3600000*24*day);
// }
can’t be bothered explaining it – just trust that it’s right 
