add new function to object
<p>If I have :</p>

<pre><code>  function myFunc(a)
  {
    if(! (this instanceof myFunc) ) return new myFunc(a);
    this.myVar = "FOOBAR";
  }
</code></pre>

<p>How to make this to work? :</p>

<pre><code>  myFunc(function() { alert(this.myVar )}); // output must be "FOOBAR";
</code></pre>
