Executing JavaScript in the <head>, getElementById returns null
<p>I have following code</p>

<pre><code>&lt;html&gt;
&lt;head&gt;
&lt;script language="JavaScript"&gt;

function foo(q) {
    this.run=function(color){
        var x=document.getElementById("ff");
        alert(x); // &lt;----x=null
    };

}

var q=new foo();
q.run("yellow");
&lt;/script&gt;
&lt;/head&gt;
&lt;body&gt;

&lt;div id="ff"&gt;&lt;/div&gt;

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

<p>does anyone has idea why <code>x=null</code></p>
