Change label based on selected dropdown [Ruby on Rails 4.2]

my SO Link
http://stackoverflow.com/questions/37416737/change-label-based-on-selected-dropdown-ruby-on-rails-4-2

I have a table called network it has the column type and number.

I use this select_tag to get a list of all my network names:

<%= select_tag('NetworksList',
options_from_collection_for_select(Network.all, :id, :name))%>

I also have 2 label fields that I want to populate with information
dynamically:

<p>Network Type: <%= content_tag('span', "", id: 'NetworkType') %></p>
<p>Network Number: <%= content_tag('span', "", id: 'NetworkNumber')
%></p>

When the user selects a network from the dropdown list of network names,
I want to show the selected item's type and number in the fields named
NetworkType and NetworkNumber. I would like this to render in the view
immediately after the user selects a dropdown. How would I do this?

I am getting the current error in js console,
TypeError: network_details[network_index] is undefined
help?