Datepicker default date set to last week

Datepicker default date set to last week

I have a fromDate and a toDate input box both populated using the date picker. For the default Date how can i specify it so it always uses last week starting from Saturday and going to Sunday and not the current date or a fixed date? 

defaultDate: '-1w',

i was trying something like this 

var date = new Date();
date.setMonth(date.getMonth() + 1, 1);

but for the date not the month,  couldn't get it working, anyhelp?

Thank You.