I've developed a website in Sinatra, but at the last minute I've been told it will need a form with a datetime field (for an Activerecord object). In Rails I would just use the datetime_select helper to construct this field in the view, but I'm having trouble finding a library or extension that provides similar functionality in Sinatra. I could always roll my own, but I'm sure someone has encountered this problem before and probably has a better solution. Any suggestions?
Although Rails may have a method for this (what doesn't it have a method for?) this doesn't seem like a question in the domain of Sinatra. It sounds like you're asking how to create a custom HTML+CSS+JS widget, which is separate from the server-side code.
Unless I'm misunderstanding your question, it seems like this question is appropriate:
jQuery Date/Time Picker