Week numbers in JavaScript

How to get the week number from a date

The code below adds two new functions to the Date object. Add this to your source code.

To get the ISO week number (1-53) of a Date object, mydate, use mydate.getWeek().

To get the corresponding four-digit year, use mydate.getWeekYear().

// This script is released to the public domain and may be used, modified and // distributed without restrictions. Attribution not necessary but appreciated. // Source: https://weeknumber.net/how-to/javascript // Returns the ISO week of the date. Date.prototype.getWeek = function() { var date = new Date(this.getTime()); date.setHours(0, 0, 0, 0); // Thursday in current week decides the year. date.setDate(date.getDate() + 3 - (date.getDay() + 6) % 7); // January 4 is always in week 1. var week1 = new Date(date.getFullYear(), 0, 4); // Adjust to Thursday in week 1 and count number of weeks from date to week1. return 1 + Math.round(((date.getTime() - week1.getTime()) / 86400000 - 3 + (week1.getDay() + 6) % 7) / 7); } // Returns the four-digit year corresponding to the ISO week of the date. Date.prototype.getWeekYear = function() { var date = new Date(this.getTime()); date.setDate(date.getDate() + 3 - (date.getDay() + 6) % 7); return date.getFullYear(); }

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