Why can't I overwrite the prototype of `Array` (`Array.prototype`)?
<p>I set the prototype of <code>Array</code> as an instance of <strong><code>my</code></strong>, I think <code>book.aa</code> will display <code>"aa"</code>, but it displays <code>"undefined"</code>, why? Thanks!</p>

<pre><code>   &lt;html&gt;
    &lt;head&gt;
        &lt;title&gt;Array Properties&lt;/title&gt;
        &lt;h2&gt;Array Properties&lt;/h2&gt;
        &lt;script type="text/javascript"&gt;
            function my() {
                this.aa = 'aa';
            }
            Array.prototype = new my();
            Array.prototype.bb = "bb";
            var book = new Array();  
            book[0] = "War and Peace";  

        &lt;/script&gt;
    &lt;/head&gt;
    &lt;body bgcolor="lightblue"&gt;
        &lt;script type="text/javascript"&gt;
            document.write(book.aa+book.bb);
        &lt;/script&gt;
    &lt;/body&gt;

    &lt;/html&gt;
</code></pre>
