tborychowski/get_week_number.js

## get_week_number.js
//Returns ISO 8601 week number and year
Date.prototype.getFullWeek = function(){
    var jan1, w, d = new Date(this);
    d.setDate(d.getDate()+4-(d.getDay()||7));		// Set to nearest Thursday: current date + 4 - current day number, make Sunday's day number 7
    jan1 = new Date(d.getFullYear(),0,1);		// Get first day of year
    w = Math.ceil((((d-jan1)/86400000)+1)/7);		// Calculate full weeks to nearest Thursday
    return {y: d.getFullYear(), w: w };
};
//Returns ISO 8601 week number
Date.prototype.getWeek = function(){
	return this.getFullWeek().w;
};
var getWeeksInYear = function(y){
	return new Date(y,11,28).getFullWeek().w;
};
	//Returns ISO 8601 week number and year
	Date.prototype.getFullWeek = function(){
	var jan1, w, d = new Date(this);
	d.setDate(d.getDate()+4-(d.getDay()\|\|7)); // Set to nearest Thursday: current date + 4 - current day number, make Sunday's day number 7
	jan1 = new Date(d.getFullYear(),0,1); // Get first day of year
	w = Math.ceil((((d-jan1)/86400000)+1)/7); // Calculate full weeks to nearest Thursday
	return {y: d.getFullYear(), w: w };
	};
	//Returns ISO 8601 week number
	Date.prototype.getWeek = function(){
	return this.getFullWeek().w;
	};
	var getWeeksInYear = function(y){
	return new Date(y,11,28).getFullWeek().w;
	};