title: How can I extend D3?
body: <p>Is there an API for extending D3 like with jQuery? With jQuery we are able to extend it like this: </p>
  
  <pre><code>$.fn.myExtnesion = function () {  
      return $(this).each(function myPlugincode(){
      });
  };
  </code></pre>
  
  <p>Is there a similar API for D3? </p>