What is the "!!" operator in Javascript?
<blockquote>
  <p><strong>Possible Duplicate:</strong><br>
  <a href="http://stackoverflow.com/questions/784929/what-is-the-operator-in-javascript">What is the !! operator in JavaScript?</a>  </p>
</blockquote>



<p>Sorry if this one is obvious but I can't google it</p>

<p>What is the "!!" operator in Javascript?
e.g </p>

<p><code>
if (!!window.EventSource) {
  var source = new EventSource('stream.php');
} else {
  // Result to xhr polling :(
}
</code>  </p>

<p>Did the author just use "!" twice i.e a double negation? I'm confused because this is in the official doc</p>
