How to select a date from date picker calender in nightwatch javascript automation?

I want to select a date from datepicker, that date is not static i.e. selecting same day, it should be dynamic in nature. i.e. should be able to select any past date including today.

Problem: After click on a field i get this calender, from calender i have to select a date. how to do it? preferable in Nightwatch js.