How to get first date and last date of the week from week number and year?

Question

In JavaScript I want to get first date of the week and last date of the week by week number and year only.

For example if I my input is:

2(week),2012

Then my output should be:

2012-01-08 and 2012-01-14

Answer 1

Try this:

var year = 2012;
var week = 2;
var d = new Date("Jan 01, " + year + " 01:00:00");
var w = d.getTime() + 604800000 * (week - 1);
var n1 = new Date(w);
var n2 = new Date(w + 518400000)

console.log(n1);
console.log(n2);

n1 contains the first day of the week
n2 contains the last day of the week

As for the constants:
604800000 is one week in milliseconds
518400000 is six days

Answer 2

A little change to @bardiir 's answer, if the first day of the year is not Sunday(or Monday) that result is not correct. You should minus the number of the first day.

Changed code

firstDay = new Date(2015, 0, 1).getDay();
console.log(firstDay);
var year = 2015;
var week = 67;
var d = new Date("Jan 01, " + year + " 01:00:00");
var w = d.getTime() - (3600000 * 24 * (firstDay - 1)) + 604800000 * (week - 1)
var n1 = new Date(w);
var n2 = new Date(w + 518400000)

console.log(n1.toString());
console.log(n2.toString());

if you wish the first is Sunday, change (firstDay-1) to firstDay