Find beginning of week date

gistfile1.js

var someDate = new Date();
var n = someDate.getDay();
someDate.setDate(someDate.getDate()-n);
var dd = someDate.getDate();
var mm = someDate.getMonth() + 1;
var y = someDate.getFullYear();
var someFormattedDate = mm + '/'+ dd + '/'+ y;

alert('start week: '+someFormattedDate);