Ways to Detect whether AngularJS is loaded in the current page or not

How can I detect whether AngularJS is loaded in the current page or not. I want to load AngularJS from CDN and in case if it fails I want to load from LocalServer. The following script does that for JQuery

    <script src="//ajax.googleapis.com/ajax/libs/jquery/1.8.2/jquery.min.js"></script>
<script>window.jQuery || document.write('<script src="libs/jquery-1.8.2.min.js"><\/script>')</script>

Is there a similiar way for AngularJS.