Javascript Date prototypes for finding the beginning and end of days and weeks. Beginning of the week is defined as Sunday

date.coffee

Date::beginningOfMonth = ->
  beginningOfMonth = @beginningOfDay()
  beginningOfMonth.setDate(1)
  beginningOfMonth

Date::endOfMonth = ->
  endOfMonth = @endOfDay()
  endOfMonth.setMonth(endOfMonth.getMonth() + 1)
  endOfMonth.setDate(0)
  endOfMonth

Date::endOfWeek = ->
  daysToSaturday = if @getDay() != 6 then 6 - @getDay() else 0

  endOfWeek = new Date(@)
  endOfWeek.setDate(@getDate() + daysToSaturday)
  endOfWeek.endOfDay()

Date::beginningOfWeek = ->
  daysToSunday = if @getDay() != 0 then @getDay() else 0

  beginningOfWeek = new Date(@)
  beginningOfWeek.setDate(@getDate() - daysToSunday)
  beginningOfWeek.beginningOfDay()

Date::endOfDay = ->
  new Date(@getFullYear(), @getMonth(), @getDate(), 23, 59, 59, 999)

Date::beginningOfDay = ->
  new Date(@getFullYear(), @getMonth(), @getDate(), 0, 0, 0, 0)