var exists or var gets value syntax?
<p>I came across the following line of code in the underscore.js source:</p>

<pre><code>function (obj, iterator, context) {
  iterator || (iterator = _.identity);
  ...
}
</code></pre>

<p>Is that syntax equivalent to:</p>

<pre><code>if (!iterator) {
  iterator = _.identity;
}
</code></pre>

<p>Are there any performance benefits to using the former syntax other than reducing the statement to one line?</p>
