window.event !== window.event in IE
<p><strong>Code：</strong></p>

<pre><code>&lt;html&gt;
&lt;head&gt;
&lt;script type="text/javascript"&gt;
  onload = function(){
    document.getElementById('btn1').onclick = function(){   
      if (window === window)  
        alert('window === window')
      else
        alert('window !== window');

      if (window.event === window.event)  
        alert('window.event === window.event')
      else
        alert('window.event !== window.event' );   
    }
  }
&lt;/script&gt;
&lt;/head&gt;
&lt;body&gt;
&lt;button id="btn1" &gt;click&lt;/button&gt;
&lt;/body&gt;
&lt;/html&gt;
</code></pre>

<p><strong>Result:</strong></p>

<p>IE(i have tested IE6 - IE8) says:</p>

<pre><code>window === window
window.event !== window.event
</code></pre>

<p>All other browsers say:</p>

<pre><code>window === window
window.event === window.event
</code></pre>

<p>What's the reason for IE's response? Thanks.</p>
