Rails - dynamically add multiple fields of nested forms

Is there a way to dynamically add X the number of nested form fields? For example, if we have a selection menu:

Select Menu -1 -2 -3 -4

And the user selects 3, then creates 3 nested form fields.

I looked at the Railscast form on a nested model, but for me it already has one set of fields for already created ones and just inserts them every time a link is clicked. I would like to dynamically insert the quantity X every time the selection menu changes.

Here is the code from Railscast:

def link_to_add_fields(name, f, association)
  new_object = f.object.send(association).klass.new
  id = new_object.object_id
  fields = f.fields_for(association, new_object, child_index: id) do |builder|
    render(association.to_s.singularize + "_fields", f: builder)
  end
  link_to(name, '#', class: "add_fields", data: {id: id, fields:  fields.gsub("\n", "")})
end