Strange javascript operator: expr >>> 0
<p>the following function is designed to implement the <code>indexOf</code> property in IE. If you've ever had to do this, I'm sure you've seen it before.</p>

<pre><code>if (!Array.prototype.indexOf){

  Array.prototype.indexOf = function(elt, from){

    var len = this.length &gt;&gt;&gt; 0;
    var from = Number(arguments[1]) || 0;

    from = (from &lt; 0)
         ? Math.ceil(from)
         : Math.floor(from);

    if (from &lt; 0)
      from += len;

    for (; from &lt; len; from++){
      if (from in this &amp;&amp;    
          this[from] === elt)
        return from;
    }

    return -1;    
  };
}
</code></pre>

<p>I'm wondering if it's common to use three greater than signs as the author has done in the initial length check?    </p>

<p><code>var len = this.length &gt;&gt;&gt; 0</code></p>

<p>Doing this in a console simply returns the length of the object I pass to it, not true or false, which left me pondering the purpose of the syntax. Is this some high-level JavaScript Ninja technique that I don't know about? If so, please enlighten me!</p>
