function bounce() {
	d = document.periodsel;

	var bog = new Array();
	bog = d.date1a.value.split("-");
	ra = bog[0];
	re = bog[1]-1;
	ro = bog[2];

	dod = new Date(ra,re,ro);
	domo = dod.getMonth()+1;
	doda = dod.getDate()+6;

	if(doda <= '9')
		doda = '0'+doda;

	ere = dod.getFullYear()+'-'+domo+'-'+doda;

	d.date1b.value = ere;
	return true;
}

Jump a week from another date

date

JavaScript