Deleting completed items from Reminders app on macOS

DeleteCompletedReminders.scpt

--
-- This script will delete all completed items from the Reminders app
--
tell application "Reminders"
	-- retrieve the list of Reminder containers
	set reminderLists to container of reminders
	
	-- examine each Reminder container
	repeat with currentList in reminderLists
		-- retrieve the list of completed tasks
		set completedItems to (reminders in currentList whose completed is true)
		
		-- if found, then delete completed tasks
		if (count of completedItems) > 0 then		
			repeat with completedItem from 1 to count of completedItems
				delete item completedItem of completedItems
			end repeat
		end if
		
	end repeat
end tell