title: Simple extension method in TypeScript
body: <p>I'm trying to create an extension method for class but seems something is wrong. Below is the code, the output JS-file is correct but the compiler twice times shows an error <strong>"test.ts(10,16): The property 'close' does not exist on value of type 'Test'"</strong>
  What should be corrected ?</p>
  
  <pre><code>class Test {
  } 
  
  interface Test
  {
      close():any;
  }
  
  Test.prototype.close  = function() {}
  
  var t = new Test();
  
  t.close();
  </code></pre>
  
  <p><strong>Update</strong>: The code above is compiled okay with built-in types. I need to extend my own classes.</p>
  
  <p><strong>Update 2</strong>: Old compiler version issue. Currently all is okay!</p>