Array's lastIndexOf returns -1 when start is undefined
<p>in javascript,Array instance has two methods,</p>

<pre><code>[].indexOf(searchvalue [,start])
</code></pre>

<p>and</p>

<pre><code>[].lastIndexOf(searchvalue [,start])
</code></pre>

<p>is behaves strange if the "start" param is undefined:</p>

<pre><code>[1,2,3].lastIndexOf(2) // 1
[1,2,3].lastIndexOf(2,undefined) // -1
[1,2,3].indexOf(2,undefined) // 1
</code></pre>

<p>this happens in chrome and firefox,so what's the theory of the indexOf and lastIndexOf treat "undefined" differently </p>
