Created
February 7, 2019 13:22
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javascript, js, getWeek
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/** | |
* Returns the week number for this date. dowOffset is the day of week the week | |
* "starts" on for your locale - it can be from 0 to 6. If dowOffset is 1 (Monday), | |
* the week returned is the ISO 8601 week number. | |
* @param int dowOffset | |
* @return int | |
*/ | |
Date.prototype.getWeek = function (dowOffset) { | |
/*getWeek() was developed by Nick Baicoianu at MeanFreePath: http://www.meanfreepath.com */ | |
dowOffset = typeof(dowOffset) == 'int' ? dowOffset : 0; //default dowOffset to zero | |
var newYear = new Date(this.getFullYear(),0,1); | |
var day = newYear.getDay() - dowOffset; //the day of week the year begins on | |
day = (day >= 0 ? day : day + 7); | |
var daynum = Math.floor((this.getTime() - newYear.getTime() - | |
(this.getTimezoneOffset()-newYear.getTimezoneOffset())*60000)/86400000) + 1; | |
var weeknum; | |
//if the year starts before the middle of a week | |
if(day < 4) { | |
weeknum = Math.floor((daynum+day-1)/7) + 1; | |
if(weeknum > 52) { | |
nYear = new Date(this.getFullYear() + 1,0,1); | |
nday = nYear.getDay() - dowOffset; | |
nday = nday >= 0 ? nday : nday + 7; | |
/*if the next year starts before the middle of | |
the week, it is week #1 of that year*/ | |
weeknum = nday < 4 ? 1 : 53; | |
} | |
} | |
else { | |
weeknum = Math.floor((daynum+day-1)/7); | |
} | |
return weeknum; | |
}; |
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