How can I send the select box value to javascript in rails - ruby-on-rails

Question

I got the following code, which I want when people choose the OPTIONS, then show the Add an option button
<%= f.fields_for :questions do |question_form| %>
<%= question_form.text_field :question_text %>
<%= question_form.select :question_type, [ 'TEXT', 'OPTIONS', 'UPLOAD' ], :prompt => 'Select One', :id => "my_id", :onchange => "myFunction()" %>
<%= question_form.link_to_remove "Remove this Question" %>
<%= question_form.fields_for :options do |option_form| %>
<%= option_form.text_field :option_text %>
<%= option_form.link_to_remove "Remove this option" %>
<% end %>
<p id = "test" hidden><%= question_form.link_to_add "Add a option", :options %></p>
<script>
function myFunction(){
var x = document.getElementById("my_id").value;
if (x == "OPTIONS") {
document.getElementById("test").hidden = false;
}
}
</script>
<% end %>

Answer 1

First of all, you can't send a value from Rails to Js during Js execution. In that moment you are already in the browser context unless you ask something via Ajax to your server.
In this case everything can and has to be done in your browser context. Just change this line:
var x = document.getElementById("my_id").value
For:
var e = document.getElementById("my_id");
var x = e.options[e.selectedIndex].value;
This should do the trick.