title: Checking if Class type is available in Javascript Namespace
body: <p>I would like to check if a class type is even instantiable before attempting to instantiate it via the new keyword in javascript.</p>
  
  <p>For example</p>
  
  <p><code>
  var geocoder = new GClientGeocoder();
  </code>
  <br/>
  will fail if the GClientGeocoder class is not available in the namespace.</p>
  
  <p>What's the javascript idiomatic way to do this?</p>