Method Date.getISOWeek

Return the ISO week number of the year of a date.

• Syntax Number Date.getISOWeek([ Boolean utc ])
  
  The ISO 8601 standard counts the weeks of the year consecutive starting from 1. Week 1 is defined as 'the week which contains January the forth'. If utc is set to true the universal time is used; otherwise the local time is used.
• Parameters

  Boolean utc (Optional)

  Set to true to use UTC.

• Return value The ISO week number of the year.
• Examples

  To get the week number of the 24th December 2008

  // Create the date
  var d = new Date(2008,11,24);
  // Output is 52
  var w = d.getISOWeek();

• Related Date.format   Date.setISOWeek   
• Resources See ISO 8601 at Wikipedia.org if you are curious about how week numbers are defined.
  
  
  The algorithm for calculating week numbers is taken from the calendar FAQ of Claus Tøndering. If you ever wanted to know anything about calendars this is the place to start.
• Download
  Download this function including dependencies
  Source

  Unless otherwise noted all code in the JSLab Standard Library is licensed as GPLv3. See http://www.gnu.org/licenses/gpl.html for the entire license.

  // ************************************************************************** // Copyright 2007 - 2009 Tavs Dokkedahl // Contact: http://www.jslab.dk/contact.php // // This file is part of the JSLab Standard Library (JSL) Program. // // JSL is free software; you can redistribute it and/or modify // it under the terms of the GNU General Public License as published by // the Free Software Foundation; either version 3 of the License, or // any later version. // // JSL is distributed in the hope that it will be useful, // but WITHOUT ANY WARRANTY; without even the implied warranty of // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the // GNU General Public License for more details. // // You should have received a copy of the GNU General Public License // along with this program. If not, see <http://www.gnu.org/licenses/>. // *************************************************************************** // Get ISO week number of the year // The algorithm is credit to Claus Tøndering and is taken from his calendar FAQ // See http://www.tondering.dk/claus/cal/node8.html#SECTION00880000000000000000 // for more information // Integer division: a/b|0 Date.prototype.getISOWeek = function(utc) { var y = utc ? this.getUTCFullYear(): this.getFullYear(); var m = utc ? this.getUTCMonth() + 1: this.getMonth() + 1; var d = utc ? this.getUTCDate() : this.getDate(); // If month jan. or feb. if (m < 3) { var a = y - 1; var b = (a / 4 | 0) - (a / 100 | 0) + (a / 400 | 0); var c = ( (a - 1) / 4 | 0) - ( (a - 1) / 100 | 0) + ( (a - 1) / 400 | 0); var s = b - c; var e = 0; var f = d - 1 + 31 * (m - 1); } // If month mar. through dec. else { var a = y; var b = (a / 4 | 0) - ( a / 100 | 0) + (a / 400 | 0); var c = ( (a - 1) / 4 | 0) - ( (a - 1) / 100 | 0) + ( (a - 1) / 400 | 0); var s = b - c; var e = s + 1; var f = d + ( (153 * (m - 3) + 2) / 5 | 0) + 58 + s; } var g = (a + b) % 7; // ISO Weekday (0 is monday, 1 is tuesday etc.) var d = (f + g - e) % 7; var n = f + 3 - d; if (n < 0) var w = 53 - ( (g - s) / 5 | 0); else if (n > 364 + s) var w = 1; else var w = (n / 7 | 0) + 1; return w; };