// How many calendar weeks does February 2015 span?
var result = getWeeksInMonth(new Date(2015, 1, 8))
//=> 4
// If the week starts on Monday,
// how many calendar weeks does July 2017 span?
var result = getWeeksInMonth(new Date(2017, 6, 5), { weekStartsOn: 1 })
//=> 6