Collection_select with optional text box

I have a form that prompts a user to select an option from a drop down
selection box. Ideally I’d like a text box to appear next to the
selection box only if they select “Add new”. I’ve been able to do this
in the past with the select helper but I haven’t been able to get
collection_select to work.

I’ve tried a few different things but my latest iteration looks like

<div class="field" >
  <%= f.fields_for :reviews do |c| %>
     <%= c.collection_select(:review, Review.order(:review), :id,

include_blank: true, :prompt => “add select”, :onchange
<%= c.text_field :review, review: “class-show”, style:
“display: none;”%>

<% end %>

review-dropdown = function(){
if(this.value == “Add New”) {

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