Javascript date functions

date.js

Date.prototype.asStartOfWeek = function(start) {
  start = start || 0;
  var today = new Date(this.setHours(0, 0, 0, 0));
  var day = today.getDay() - start;
  var date = today.getDate() - day + (day == 0 ? -6 : 1);
  return new Date(today.setDate(date));
}

Date.prototype.asEndOfWeek = function(start) {
  start = start || 0;
  var today = new Date(this.setHours(23, 59, 59, 999));
  var day = today.getDay() - start;
  var date = today.getDate() - day + (day == 0 ? -6 : 1);
  return new Date(today.setDate(date + 6));
}

Date.prototype.withinTheWeekOf = function(weekDate) {
  return this.getTime() >= weekDate.asStartOfWeek().getTime() && this.getTime() <= weekDate.asEndOfWeek().getTime();
}