一个好用的JS日期函数

/**
 * 根据给定的日期得到该日期的相关信息
 *
 * @param dateObj:日期对象
 *
 * @return daysInYear：当前日期在今年中是第几天
 * @return weekInYear：当前日期所在今年是第几周
 * @return weekInMonth：当前日期在今年这个月份是第几周
 * @return weekStartDate：当前日期所在周的星期一的日期
 * @return weekEndDate：当前日期所在周的周日的日期
 */
function DateToWeekFormat(dateObj)
{
    var year = dateObj.getFullYear();
    var month = dateObj.getMonth();

    var date = dateObj.getDate();
    var day = dateObj.getDay();
    var hr = dateObj.getHours();
    var min = dateObj.getMinutes();
    var sec = dateObj.getSeconds();
    var daysInYear = Math.ceil((dateObj-new   Date(year,0,0))/86400000);
    var weekInYear = Math.ceil((daysInYear+new   Date(year,0,1).getDay())/7);
    var weekInMonth = Math.ceil((date+new   Date(year,month,1).getDay())/7);
    var weekStartDate = new Date(dateObj-(dateObj.getDay()-1)*86400000);
    var weekEndDate =new Date((weekStartDate/1000+6*86400)*1000);

    return {daysInYear:daysInYear,weekInYear:weekInYear,weekInMonth:weekInMonth,weekStartDate:weekStartDate,weekEndDate:weekEndDate};
}