Javascript - how do i set the 'this' variable for a function
<p>I have a function which takes a callback function.  How can I set the 'this' variable of the callback function?</p>

<p>eg.</p>

<pre><code>function(fn){
    //do some stuff
    fn(); //call fn, but the 'this' var is set to window
    //, how do I set it to something else
}
</code></pre>
