collection_select with select2 and bootstrap: undefined is not a function - ruby-on-rails

Question

In a Rails 4.1 app, I have a collection select that is loaded from a hash. I would like to use the select2 boostrap styling, but it doesn't seem to be working.
I have included the select2-rails gem, and updated application.js and application.css as per the instructions.
gem 'select2-rails'
//= require select2
*= require select2
*= require select2-bootstrap
The collection_select is loaded from a constant on the model. I don't think this is especially relevant to the issue, but added it here in case it helps someone.
FLASHCARD_TYPE = {"verb" => "Verb Conjugation",
"name" => "Word",
"number" => "Number",
"quiz" => "Quiz"}
Rails view
<div class="form-group">
<%= f.label :card_type, :class => "col-sm-2 control-label" %>
<div class="col-sm-2">
<%= f.collection_select(:card_type, Flashcard::FLASHCARD_TYPE, :first, :last) %>
</div>
</div>
app/assets/javascripts/application.js
$(document).ready(function(){
$("#flashcard_card_type").select2();
});
The rendered html shows the select2 javascript, and the select shows as:
<div class="form-group">
<label class="col-sm-2 control-label" for="flashcard_card_type">Card type</label>
<div class="col-sm-2">
<select id="flashcard_card_type" name="flashcard[card_type]">
<option value="verb">Verb Conjugation</option>
<option value="name">Word</option>
<option value="number">Number</option>
<option value="quiz">Quiz</option></select>
</div>
</div>
How can this to work properly?
In fact I would also like the option to have a site-wide default for all selects via class, then the ability to override styling by individual id.
I thought this would work as site-wide for all selects, but it also does nothing.
$(document).ready(function(){
$("select").select2();
});
EDIT
As recommended by #San I checked the Javascript console, and got
Uncaught TypeError: undefined is not a function
This the code it failed on
$(document).ready(function(){
$("#flashcard_card_type").select2();
});
EDIT 2
Full application.js file
//= require jquery
//= require jquery_ujs
//= require bootstrap-sprockets
//= require bootstrap-markdown
//= require select2
//= require_tree .
$(document).ready(function(){
$("#flashcard_card_type").select2();
});
EDIT 3
jQuery is finding the element OK
$(document).ready(function(){
debugger;
console.log($("#flashcard_card_type"))
$("#flashcard_card_type").select2();
});
log
[select#flashcard_card_type, context: document, selector: "#flashcard_card_type", jquery: "1.11.1", constructor: function, toArray: function…]
0: select#flashcard_card_type
context: document
length: 1
selector: "#flashcard_card_type"
__proto__: Object[0]
EDIT - What I have tried
removed turbolinks
added the javascript to the page
deleted cache, restarted rails
What I have found
jQuery can find the tag
The select2 library is loaded via the network tab in the js debugger
Any ideas?

Answer 1

Just wondering. Did you run bundle install after adding the gem to the Gemfile?
If you did, the last thing to check is to make sure select2 JavaScript file is loading before your block to use it. Verify that by doing view source on the page and make sure select2.js is listed before application.js file (assuming you are in dev mode).