title: Define getter/setter on existing object w/ TypeScript
body: <p>How would I write the following code using TypeScript?</p>
  
  <pre><code>document.__defineGetter__('cookie', function() { ... });
  document.__defineSetter__('cookie', function(v) { ... });
  </code></pre>
  
  <p>Thanks in advance!</p>
  
  <p>(p.s. this assumes <code>document</code> exists, but <code>document.cookie</code> does not... )</p>