问题
How should the getWeekNumber() prototype should be changed for Date class if I have a custom week start day instead of Monday.
Current code for finding ISO Week Number:
Date.prototype.getWeekNumber = function() {
// Create a copy of this date object
var target = new Date(this.valueOf());
// ISO week date weeks start on monday
// so correct the day number
var dayNr = (this.getDay() + 6) % 7;
// ISO 8601 states that week 1 is the week
// with the first thursday of that year.
// Set the target date to the thursday in the target week
target.setDate(target.getDate() - dayNr + 3);
// Store the millisecond value of the target date
var firstThursday = target.valueOf();
// Set the target to the first thursday of the year
// First set the target to january first
target.setMonth(0, 1);
// Not a thursday? Correct the date to the next thursday
if (target.getDay() !== 4) {
target.setMonth(0, 1 + ((4 - target.getDay()) + 7) % 7);
}
// The weeknumber is the number of weeks between the
// first thursday of the year and the thursday in the target week
return 1 + Math.ceil((firstThursday - target) / 604800000); // 604800000 = 7 * 24 * 3600 * 1000
};
回答1:
Use your existing function and add an optional parameter weekstart
that specifies on which weekday a week starts: 0 is Sunday, 1 is Monday and so on. The default value is Monday.
Date.prototype.getWeekNumber = function(weekstart) {
var target = new Date(this.valueOf());
// Set default for weekstart and clamp to useful range
if (weekstart === undefined) weekstart = 1;
weekstart %= 7;
// Replaced offset of (6) with (7 - weekstart)
var dayNr = (this.getDay() + 7 - weekstart) % 7;
target.setDate(target.getDate() - dayNr + 3);
var firstThursday = target.valueOf();
target.setMonth(0, 1);
if (target.getDay() !== 4) {
target.setMonth(0, 1 + ((4 - target.getDay()) + 7) % 7);
}
return 1 + Math.ceil((firstThursday - target) / 604800000);
};
来源:https://stackoverflow.com/questions/23781366/date-get-week-number-for-custom-week-start-day